Novel nucleic acid sequences and their use in methods for achieving pathogen resistance in plants

ABSTRACT

The invention relates to novel RacB cDNA sequences from barley and to expression cassettes and vectors comprising these promoter sequences. The invention furthermore relates to transgenic plants transformed with these expression cassettes or vectors, to cultures, parts or transgenic propagation material derived from them, and to their use for the production of foodstuffs, feeding stuffs, seed, pharmaceuticals or fine chemicals. The invention furthermore relates to methods of generating or increasing a pathogen resistance in plants by reducing the expression of an RacB protein or of a functional equivalent thereof.

The invention relates to novel RacB cDNA sequences from barley and to expression cassettes and vectors comprising these sequences. The invention furthermore relates to transgenic plants transformed with these expression cassettes or vectors, to cultures, parts or transgenic propagation material derived from them, and to their use for the production of foodstuffs, feeding stuffs, seed, pharmaceuticals or fine chemicals. The invention furthermore relates to methods of generating or increasing a pathogen resistance in plants by reducing the expression of an RacB protein or of a functional equivalent thereof.

The aim of plant biotechnology work is the generation of plants with advantageous novel properties, for example for increasing agricultural productivity, increasing the quality in the case of foodstuffs, or for producing specific chemicals or pharmaceuticals (Dunwell J M (2000) J Exp Bot 51 Spec No:487-96). The plant's natural defense mechanisms against pathogens are frequently insufficient. Fungal diseases alone result in annual yield losses of many billions of US$. The introduction of foreign genes from plants, animals or microbial sources can increase the defenses. Examples are the protection of tobacco against feeding damage by insects by expressing Bacillus thuringiensis endotoxins under the control of the ³⁵S CaMV promoter (Vaeck et al. (1987) Nature 328:33-37) or the protection of tobacco against fungal infection by expressing a bean chitinase under the control of the CaMV promoter (Broglie et al. (1991) Science 254:1194-1197). However, most of the approaches described only offer resistance to a single pathogen or a narrow spectrum of pathogens.

Only a few approaches exist which impart a resistance to a broader spectrum of pathogens, in particular fungal pathogens, to plants. Systemic acquired resistance (SAR)—a defense mechanism in a variety of plant/pathogen interactions—can be mediated by the application of endogenous messenger substances such as jasmonate (JA) or salicylic acid (SA) (Ward, et al. (1991) Plant Cell 3:1085-1094; Uknes, et al. (1992) Plant Cell 4(6):645-656). Similar effects can also be achieved by synthetic compounds such as 2,6-dichloroisonicotinic acid (INA) or S-methyl benzo(1,2,3)thiadiazole-7-thiocarboxylate (BTH; Bion®) (Friedrich et al. (1996) Plant J 10(1):61-70; Lawton et al. (1996) Plant J. 10:71-82). The expression of pathogenesis-related (PR) proteins, which are highly regulated in the case of an SAR, may also cause pathogen resistance in some cases.

In barley, the Mlo locus has been described for some time as a negative regulator of plant defense. The loss, or loss of function, of the Mlo gene causes an increased and, above all, race-unspecific resistance for example against a large number of mildews (Büschges R et al. (1997) Cell 88:695-705; Jorgensen J H (1977) Euphytica 26:55-62; Lyngkjaer M F et al. (1995) Plant Pathol 44:786-790). The Mlo phenotype is inherited recessively, which also suggests a function as a susceptibility gene. Mlo-deficient barley varieties obtained by traditional breeding are already being widely used in agriculture. Although these varieties are being grown intensively, this resistance has proved to be extraordinarily durable, probably owing to the recessivity. Resistance breakdown has not been observed as yet. Mlo-like resistances in other plants, especially in cereal species, have not been described even though wheat, rye and other cereals are also attacked by comparable mildew pathogens. The reason in the case of wheat may be, for example, the existence of a hexaploid genome, which makes the identification of mutants in which each of the six copies of the gene has been inactivated extremely difficult.

The Mlo gene has only recently been cloned (Büschges R et al. (1997) Cell 88:695-705; WO 98/04586; Schulze-Lefert P, Vogel J (2000) Trends Plant Sci. 5:343-348). As a consequence, various homologs have been isolated from other cereal species. Various methods for obtaining pathogen resistance using these genes have been described (WO 98/04586; WO 00/01722; WO 99/47552).

Mlo resistance of a plant to mildew pathogens manifests itself in two important events, both of which bring about resistance to penetration: cell wall apposition (CWA) underneath the penetration site of the pathogen in the epidermal cell wall. Spreading of this fungal pathogen is almost exclusively restricted to this subcellular structure (Jorgensen J H and Mortensen K (1977) Phytopathology 67:678-685; Freialdenhoven A et al. (1996) Plant Cell 8:5-14). This reaction is caused by the genes Ror1 and Ror2, which are required for the effect of Mlo (Peterhänsel C et al. (1997) 9:1397-1409).

The disadvantage in Mlo pathogen resistance is that Mlo-deficient plants—even in the absence of a pathogen—initiate a defense mechanism which manifests itself for example in the spontaneous death of leaf cells (Wolter M et al. (1993) Mol Gen Genet 239:122-128). A further disadvantage is that the Mlo-deficient genotypes are hypersusceptible to hemibiotrophic pathogens such as Magnaporte grisea (M. grisea) and Cochliobolus sativus (Bipolaris sorokiniana) (Jarosch B et al. (1999) Mol Plant Microbe Interact 12:508-514; Kumar J et al. (2001) Phytopathology 91:127-133). The Mlo gene therefore appears to be a negative regulator of cell death. Again, the cause is probably the induction of cell death in the absence of the Mlo gene, which increases the susceptibility to these fairly necrotrophic pathogens. This ambivalent effect, which limits the biotechnological use of Mlo, is probably due to the fact that necrotrophic fungi are capable of exploiting the more pronounced HR of the Mlo-deficient host plant for their infection process. A resistance comparable to Mlo deficiency, but without the characteristic of inducing cell death, would be desirable.

The proteins Rho, Rac and Cdc42 are members of the small GTP (guanosine triphosphate) binding protein family and regulate a large number of intracellular processes as “molecular switches”, both in plant and animal organisms. As elements of signal transduction, they play an important role in the conversion of extracellular stimuli. For example, they regulate NADPH oxidase and thus the release of reactive oxygen molecules (“oxidative burst”). Animal or human Rac1 is essential for the formation of the active NADPH oxidase complex which, in turn, is important for the formation of superoxide, thus contributing to plant defense (Irani K and Goldschmidt-Clermont P J (1998) Biochem Pharmacol 55: 1339-1346). The function in plant defense in plants and animals is largely analogous (Kwong et al. (1995) J Biol Chem 270(34): 19868-19872; Dusi et al. (1996) Biochem J 314:409-412; Diekmann et al. (1994) Science 265:531-533; Purgin et al. (1997) The Plant Cell 9:2077-2091; Kleinberg et al. (1994) Biochemistry 33:2490-2495; Prigmore et al. (1995) Journal of Biol Chem 27(18): 10717-10722; Irani et al. (1997) Science 275:1649-1652; Low et al. (1994) Advances in Molecular Genetics of Plant-Microbe Interactions 3:361-369 (1994) eds. M J Daniels, Kluwer Acadmic Publishers, Netherlands; Mehdy et al. (1994) Plant Physiol 105: 467-472; Sundaresan et al. (1996) Biochem J 318:379-382). Moreover, GTP binding proteins function in restructuring the cytoskeleton and in cell transformation (Symon M. (1996) TIBS 21: 178-181), and also in the activation of transcription (Hill et al. (1995) Cell 81:1159-1170; Chandra et al. (1996) Proc Natl Acad Sci USA 93:13393-13397).

In plants, there exists a substantial family of Rac-like proteins (Winge et al. (1997) Plant Mol Biol 35:483-495), which is also termed Rop family (Lin et al. (1997) The Plant Cell 9:1647-1659). In plants, the Rac proteins appear to have a function in the release of reactive oxygen molecules as the consequence of pathogen infection (Groom Q J et al. (1996) Plant J 10: 515-522; Hassanain H H et al. (2000) Biochem Biophys Res Commun 272(3):783-788; Ono E et al. (2001) Proc Natl Acad Sci USA 98: 759-764). Rac modulates, inter alia, cell wall architecture, signal transduction in the meristem and the defense against pathogens (Valster A H et al. (2000) Trends Cell Biol 10(4):141-146). When the constitutively active form is overexpressed, Rac1 from rice is capable of inducing a hypersensitive response (HR) at the sites of M. grisea attack, thus causing pathogen resistance. Analogously, the expression of a negative dominant form of Rac1 brings about an increased susceptibility to M. grisea (Kawasaki T et al. (1999) Proc Natl Acad Sci USA 96:10922-10926; Ono E et al. (2001) Proc Natl Acad Sci USA 98: 759-764). These findings suggest that an overexpression of Rac proteins in the plant can bring about advantageous effects with regard to plant defense.

WO 00/15815 describes five Rac genes from maize. Although methods for both an up regulation and a down regulation of Rac proteins are described and speculatively discussed in connection with obtaining a resistance to pathogens (p. 55/line 25 et seq.), the only technical teaching, which describes this use in real terms, concerns merely an overexpression of the claimed Rac genes for obtaining pathogen resistance (p. 60/line 21 et seq.). The author postulates quite unambiguously and in agreement with the situation described in the prior art (p. 60/line 31 et seq.): “Thus the present invention is useful in protecting plants from pathogens. Once a plant is transformed with a polynucleotide sequence encoding an Rac polypeptide, expression of the polypeptide in the plant confers resistance to infection by plant pathogens.” The rationale behind this hypothesis (plants defense via reactive oxygen molecules) is explained hereinbelow and supported by a large number of references. Beyond this, no differentiation is being made between the five claimed Rac genes.

It is an object of the present invention to provide novel methods of plant defense against pathogens which bring about an effective defense against as broad a spectrum of pathogens as possible in as large a number of plant species as possible, preferably the crop plants used in agriculture. We have found that this object is achieved by the method according to the invention.

The invention firstly comprises a method of generating or increasing the resistance to at least one pathogen in plants, which comprises the following steps

-   a) reducing the amount, activity or function of an RacB protein in a     plant or a tissue, organ, part or cell thereof, and -   b) selecting those plants in which, as opposed or as compared to the     original plant, the resistance to at least one pathogen exists or is     increased.

Surprisingly, the Rac homolog RacB from barley (Hordeum vulgare) (SEQ ID NO: 1) (hereinbelow: hvRacB), despite a great similarity with rice Rac1, has a negative control function upon attack by powdery mildew of barley Blumeria (syn. Erysiphe) graminis f.sp. hordei (Bgh), as opposed to the former: reducing the hvRacB expression in the epidermal cell by a sequence-specific RNA interference approach using double-stranded hvRacB dsRNA (“gene silencing”) significantly prevented the development of haustoria owing to Bgh infection. Further experiments demonstrated (cf. Example 7) that this phenotype cannot be observed in an mlo5-ror1-mutant genotype, namely barley A89. This suggests that RacB is linked operably to Mlo or Ror1 or both, that is to say they probably act within a signal cascade.

Similarly to the loss of function of Mlo, that of HvRacB confers broad resistance to various Blumeria graminis f.sp. hordei isolates. In transient gene silencing experiments, HvRacB reduced the penetration efficiency (development of haustoria) of Bgh by 44% (cf. Example 7), an effect whose magnitude corresponds to the effect achieved by Mlo dsRNA (Schweizer P et al. (2000) Plant J 24:895-903). In the wild-type barley variety Ingrid, approximately 60% of the fungal penetrations resulted in the development of haustoria, while the penetration rate in BCIngrid-mlo5 is virtually 0%. The barley variety A89 (mlo-ror1 dual mutant) shows a penetration efficiency of approximately 20 to 35%. An altered RacB expression owing to Bgh inoculation was observed in none of these variants (cf. Example 7; FIG. 3). The fact that only a penetration of approximately 50% can be observed even in pathogen-sensitive wild-type varieties, such as Pallas or Ingrid, can be attributed to the basal resistance which is always present.

Interestingly, the gene silencing of hvRacB only enhances cell wall apposition, but apparently not the spontaneous cell death of the plant, which is in contrast to Mlo. Thus, HvRacB differs from OsRac1, a rice homolog of Rac1 (Ono E et al. (2001) Proc Natl Acad Sci USA 98: 759-764). HvRacB acts predominantly as negative regulator of cell wall apposition. This difference is of outstanding importance for its use for obtaining pathogen resistance in plants. As already described above, Mlo resistance to biotrophic fungi (for example mildew fungi) is indeed caused, inter alia, by increased cell wall apposition, but the trade-off is a higher susceptibility to necrotrophic fungi (Jarosch B et al. (1999) Mol Plant Microbe Interact 12:508-514; Kumar J et al. (2001) Phytopathology 91:127-133). Since HvRacB only affects cell all apposition, this problem of ambivalence can be circumvented.

Owing to the above findings, RacB must be considered as a key element for the successful penetration of a pathogen such as Bgh into the plant cell. Accordingly, the method according to the invention has all the advantages of Mlo deficiency without simultaneously showing its biggest shortcoming, namely increased spontaneous cell death.

Moreover, the method outperforms all those methods in which a pathogen-resistant phenotype is realized by overexpressing a resistance-conferring protein. Switching off a gene can be realized without expressing a (foreign) protein. In an ideal case, all that needs doing is to deactivate the endogenous gene. This has not inconsiderable advantages for approval and acceptance by the consumer, who is frequently apprehensive toward plants with foreign proteins. Very especially advantageous in this context is the use of inducible promoters for reducing the amount, activity or function of RacB protein, which, for example when using pathogen-inducible promoters, allows expression only when required (i.e. pathogen infection).

A partial sequence of the barley RacB cDNA (HvRacB-cDNA) (GenBank Acc. No.: AJ290240), which is highly conserved relative to rice RacB (GenBank Acc. No.: AF250327) and maize RacB (GenBank Acc. No.: AF126053) and very similar to rice Rac1 has been described. Maize RacB is also one of the five Rac genes in the abovementioned application WO 00/15815 (Sequence No. 3). The complete coding sequence of the HvRacB protein has not been described as yet (see Example 1). Barley RacB has a homology of 95% identity with rice RacB and maize RacB and is over 55% identical to human RAC1 or RAC2 (Hassanain et al. 2000, FIG. 1). HvRacB is expressed constitutively in primary leaves of barley (epidermis-specifically) and its expression level is not affected substantially by Bgh infection. Expression thus takes place in the tissue which interacts directly with the Bgh pathogen.

In principle, the method according to the invention can be applied to all plant species, preferably to those in which an RacB protein or a functional equivalent thereof is expressed naturally. Since the function of RacB is closely connected functionally to the Mlo gene and the latter has been identified in a large number of plants, including dicots (Devoto A et al. (1999) J Biol Chem 274(49):34993-5004), it can be assumed that RacB and its homologs are similarly widely distributed. The sequences from other plants (for example Arabidopsis thaliana) which are homologous to the RacB sequences disclosed within the scope of the present invention can be found readily for example by database searches or by screening genetic libraries using the RacB sequences as search sequence or probe.

The term “plant” as used herein refers to all genera and species of higher and lower plants of the Plant Kingdom. The term includes the mature plants, seed, shoots and seedlings and their derived parts, propagation material, plant organs, tissue, protoplasts, callus and other cultures, for example cell cultures, and any other type of plant cell grouping to give functional or structural units. Mature plants refers to plants at any desired developmental stage beyond that of the seedling. Seedling refers to a young immature plant at an early developmental stage. “Plant” comprises all annual and perennial monocotyledonous and dicotyledonous plants and includes by way of example but not by limitation those of the genera Cucurbita, Rosa, Vitis, Juglans, Fragaria, Lotus, Medicago, Onobrychis, Trifolium, Trigonella, Vigna, Citrus, Linum, Geranium, Manihot, Daucus, Arabidopsis, Brassica, Raphanus, Sinapis, Atropa, Capsicum, Datura, Hyoscyamus, Lycopersicon, Nicotiana, Solarium, Petunia, Digitalis, Majorana, Ciahorium, Helianthus, Lactuca, Bromus, Asparagus, Antirrhinum, Heterocallis, Nemesis, Pelargonium, Panieum, Pennisetum, Ranunculus, Senecio, Salpiglossis, Cucumis, Browaalia, Glycine, Pisum, Phaseolus, Lolium, Oryza, Zea, Avena, Hordeum, Secale, Triticum, Sorghum, Picea and Populus.

The term “plant” preferably comprises monocotyledonous crop plants such as, for example, cereal species such as wheat, barley, millet, rye, triticale, maize, rice, sorghum or oats and also sugar cane.

The term furthermore comprises dicotyledonous crop plants such as, for example,

-   -   Brassicacae such as oilseed rape, canola, cress, Arabidopsis,         cabbages or canola, Leguminosae such as soybean, alfalfa, pea,         beans or peanut     -   Solanaceae such as potato, tobacco, tomato, egg plant or pepper,         Asteraceae such as sunflower, Tagetes, lettuce or Calendula,     -   Cucurbitaceae such as melon, pumpkin/squash or zucchini,         and also linseed, cotton, hemp, clover, spinach, flax, red         pepper, carrot, beet, radish, sugar beet, sweet potato,         cucumber, chicory, cauliflower, broccoli, asparagus, onion,         garlic, celery/celeriac, strawberry, raspberry, blackberry,         pineapple, avocado and the various tree, bush, nut and vine         species. Tree species preferably comprise plum, cherry, peach,         nectarine, apricot, banana, papaya, mango, apple, pear, quince.

Also comprised are ornamental plants, useful trees, ornamental trees, flowers, cut flowers, shrubs or lawns such as by way of example but not by limitation the families of the Rosaceae such as rose, Ericaceae such as rhododendrons and azaleas, Euphorbiaceae such as poinsettias and croton, Caryophyllaceae such as carnations, Solanaceae such as petunias, Gesneriaceae such as African violet, Balsaminaceae such as touch-me-not, Orchidaceae such as orchids, Iridaceae such as gladioli, iris, freesia and crocus, Compositae such as calendula, Geraniaceae such as geraniums, Liliaceae such as dracaena, Moraceae such as ficus, Araceae such as philodendron and many others.

Preferred within the scope of the invention are those plants which are employed as foodstuffs or feeding stuffs, very especially preferaby monocotyledonous genera and species like the above-described cereal species.

The method is applied very especially preferably to monocotyledonous plants, most preferably to agriculturally important plants such as wheat, oats, millet, barley, rye, maize, rice, buckwheat, sorghum, triticale, spelt, linseed or sugar cane.

“Pathogen resistance” denotes the reduction or weakening of disease symptoms of a plant following infection by a pathogen. The symptoms can be manifold, but preferably comprise those which directly or indirectly have an adverse effect on the quality of the plant, the quantity of the yield, the suitability for use as feeding stuff or foodstuff, or else which make sowing, planting, harvesting or processing of the crop difficult.

“Conferring”, “existing”, “generating” or “increasing” a pathogen resistance means that the defense mechanisms of a specific plant species or variety is increasingly resistant to one or more pathogens due to the use of the method according to the invention in comparison with the wild type of the plant (“original plant”), to which the method according to the invention has not been applied, under otherwise identical conditions (such as, for example, climatic conditions, growing conditions, pathogen species and the like). The increased resistance manifests itself preferably in a reduced manifestation of the disease symptoms, disease symptoms comprising—in addition to the above-mentioned adverse effects—for example also the penetration efficiency of a pathogen into the plant or plant cells or the proliferation efficiency in or on the same. In this context, the disease symptoms are preferably reduced by at least 10% or at least 20%, especially preferably by at least 40% or 60%, very especially preferably by at least 70% or 80% and most preferably by at least 90% or 95%.

“Selection” with regard to plants in which—as opposed or as compared to the original plant—resistance to at least one pathogen exists or is increased means all those methods which a are suitable for recognizing an existing or increased resistance to pathogens. These may be symptoms of pathogen infection (for example the development of haustoria in the case of fungal infection), but may also comprise the above-described symptoms which relate to the quality of the plant, the quantity of the yield, the suitability for use as feeding stuff or foodstuff and the like.

“Pathogen” within the scope of the invention means by way of example but not by limitation viruses or viroids, bacteria, fungi, animal pests such as, for example, insects or nematodes. Especially preferred are fungi such as, for example, mildew. However, it can be assumed that a reduced expression of an RacB protein, its activity or function also brings about resistance to other pathogens. Changes in the cell wall structure can constitute a prime mechanism of pathogen resistance.

The following pathogens may be mentioned by way of example but not by limitation:

-   1. Fungal Pathogens or Fungus-Like Pathogens:

Fungal pathogens or fungus-like pathogens (e.g. Chromista) are preferably from the group comprising the Plasmodiophoramycota, Oomycota, Ascomycota, Chytridiomycetes, Zygomycetes, Basidiomycota and Deuteromycetes (Fungi imperfecti). The pathogens mentioned in Tables 1 and 2 and the diseases with which they are associated may be mentioned by way of example but not by limitation. TABLE 1 Fungal plant diseases Disease Pathogen Leag rust Puccinia recondita Yellow rust P. striiformis Powdery mildew Erysiphe graminis/Blumeria graminis Glume blotch Septoria nodorum Leaf blotch Septoria tritici Ear fusarioses Fusarium spp. Eyespot Pseudocercosporella herpotrichoides Smut Ustilago spp. Bunt Tilletia caries Take-all Gaeumannomyces graminis Anthrocnose leaf blight Colletotrichum graminicola Anthracnose stalk rot (teleomorph: Glomerella graminicola Politis); Glomerella tucumanensis (anamorph: Glomerella falcatum Went) Aspergillus ear and Aspergillus flavus kernel rot Banded leaf and sheath Rhizoctonia solani Kuhn = Rhizoctonia spot microsclerotia J. Matz (telomorph: Thanatephorus cucumeris) Black bundle disease Acremonium strictum W. Gams = Cephalosporium acremonium Auct. non Corda Black kernel rot Lasiodiplodia theobromae = Botryodiplodia theobromae Borde blanco Marasmiellus sp. Brown spot (black spot, Physoderma maydis stalk rot) Cephalosporium kernel Acremonium strictum = rot Cephalosporium acremonium Charcoal rot Macrophomina phaseolina Corticium ear rot Thanatephorus cucumeris = Corticium sasakii Curvularia leaf spot Curvularia clavata, C. eragrostidis, = C. maculans (teleomorph: Cochliobolus eragrostidis), Curvularia inaequalis, C. intermedia (teleomorph: Cochliobolus intermedius), Curvularia lunata (teleomorph: Cochliobolus lunatus), Curvularia pallescens (teleomorph: Cochliobolus pallescens), Curvularia senegalensis, C. tuberculata (teleomorph: Cochliobolus tuberculatus) Didymella leaf spot Didymella exitalis Diplodia ear rot and Diplodia frumenti (teleomorph: stalk rot Botryosphaeria festucae) Diplodia ear rot, stalk Diplodia maydis = Stenocarpella rot, seed rot and maydis seedling blight Diplodia leaf spot or Stenocarpella macrospora = Diplodialeaf streak macrospora

TABLE 2 Downy mildew Disease Pathogen Brown stripe downy Sclerophthora rayssiae var. zeae mildew Crazy top downy mildew Sclerophthora macrospora = Sclerospora macrospora Green ear downy mildew Sclerospora graminicola (graminicola downy mildew) Java downy mildew Peronosclerospora maydis = Sclerospora maydis Philippine downy mildew Peronosclerospora philippinensis = Sclerospora philippinensis Sorghum downy mildew Peronosclerospora sorghi = Sclerospora sorghi Spontaneum downy mildew Peronosclerospora spontanea = Sclerospora spontanea Sugarcane downy mildew Peronosclerospora sacchari = Sclerospora sacchari Dry ear rot (cob, Nigrospora oryzae kernel and stalk rot) (teleomorph: Khuskia oryzae) Ear rots, minor Alternaria alternata = A. tenuis, Aspergillus glaucus, A. niger, Aspergillus spp., Botrytis cinerea (teleomorph: Botryotinia fuckeliana), Cunninghamella sp., Curvularia pallescens, Doratomyces stemonitis = Cephalotrichum stemonitis, Fusarium culmorum, Gonatobotrys simplex, Pithomyces maydicus, Rhizopus microsporus Tiegh., R. stolonifer = R. nigricans, Scopulariopsis brumptii Ergot(horse's tooth) Claviceps gigantea (anamorph: Sphacelia sp.) Eyespot Aureobasidium zeae = Kabatiella zeae Fusarium ear and stalk Fusarium subglutinans = F. moniliforme rot var. subglutinans Fusarium kernel, root Fusarium moniliforme and stalk rot, seed rot (teleomorph: Gibberella fujikuroi) and seedling blight Fusarium stalk rot, Fusarium avenaceum seedling root rot (teleomorph: Gibberlla avenacea) Gibberella ear and stalk Gibberella zeae rot (anamorph: Fusarium graminearum) Gray ear rot Botryosphaeria zeae = Physalospora zeae (anamorph: Macrophoma zeae) Gray leaf spot Cercospora sorghi = C. sorghi var. (Cercospora leaf spot) maydis, C. zeae-maydis Helminthosporium root Exserohilum pedicellatum = rot Helminthosporium pedicellatum (teleomorph: Setosphaeria pedicellata) Hormodendrum ear rot Cladosporium cladosporioides = (Cladosporium rot) Hormodendrum cladosporioides, C. herbarum (teleomorph: Mycosphaerella tassiana) Hyalothyridium leaf spot Hyalothyridium maydis Late wilt Cephalosporium maydis Leaf spots, minor Alternaria alternata, Ascochyta maydis, A. tritici, A. zeicola, Bipolaris victoriae = Helminthosporium victoriae (teleomorph: Cochliobolus victoriae), C. sativus (anamorph: Bipolaris sorokiniana = H. sorokinianum = H. sativum), Epicoccum nigrum, Exserohilum prolatum = Drechslera prolata (teleomorph: Setosphaeria prolata) Graphium penicillioides, Leptosphaeria maydis, Leptothyrium zeae, Ophiosphaerella herpotricha, (anamorph: Scolecosporiella sp.), Paraphaeosphaeria michotii, Phoma sp., Septoria zeae, S. zeicola, S. zeina Northern corn leaf Setosphaeria turcica (anarnorph: blight (white blast, Exserohilum turcicum = Helminthosporium crown stalk rot, stripe) turcicum) Northern corn leaf spot Cochliobolus carbonum (anamorph: Helminthosporium ear rot Bipolaris zeicola = Helminthosporium (race 1) carbonum) Penicillium ear rot Penicillium spp., P. chrysogenum, (blue eye, blue mold) P. expansum, P. oxalicum Phaeocytostroma stalk Phaeocytostroma ambiguum, = rot and root rot Phaeocytosporella zeae Phaeosphaeria leaf spot Phaeosphaeria maydis = Sphaerulina maydis Physalospora ear rot Botryosphaeria festucae = Physalospora (Botryosphaeria ear rot) zeicola (anamorph: Diplodia frumenti) Purple leaf sheath Hemiparasitic bacteria and fungi Pyrenochaeta stalk rot Phoma terrestris = Pyrenochaeta and root rot terrestris Pythium root rot Pythium spp., P. arrhenomanes, P. graminicola Pythium stalk rot Pythium aphanidermatum = P. butleri L. Red kernel disease (ear Epicoccum nigrum mold, leaf and seed rot) Rhizoctonia ear rot Rhizoctonia zeae (teleomorph: Waitea (sclerotial rot) circinata) Rhizoctonia root rot and Rhizoctonia solani, Rhizoctonia zeae stalk rot Root rots, minor Alternaria alternata, Cercospora sorghi, Dictochaeta fertilis, Fusarium acuminatum (teleomorph: Gibberella acuminata), F. equiseti (teleomorph: G. intricans), F. oxysporum, F. pallidoroseum, F. poae, F. roseum, G. cyanogena, (anamorph: F. sulphureum), Microdochium bolleyi, Mucor sp., Periconia circinata, Phytophthora cactorum, P. drechsleri, P. nicotianae var. parasitica, Rhizopus arrhizus Rostratum leaf spot Setosphaeria rostrata, (anamorph: (Helminthosporium leaf Exserohilum rostratum = He/ disease, ear and stalk minthosporium rostratum) rot) Rust, common corn Puccinia sorghi Rust, southern corn Puccinia polysora Rust, tropical corn Physopella pallescens, P. zeae = Angiopsora zeae Sclerotium ear rot Sclerotium rolfsii Sacc. (teleomorph: (southern blight) Athelia rolfsii) Seed rot-seedling blight Bipolaris sorokiniana, B. zeicola = Helminthosporium carbonum, Diplodia maydis, Exserohilum pedicillatum, Exserohilum turcicum = Helminthosporium turcicum, Fusarium avenaceum, F. culmorum, F. moniliforme, Gibberella zeae (anamorph: F. graminearum), Macrophomina phaseolina, Penicillium spp., Phomopsis sp., Pythium spp., Rhizoctonia solani, R. zeae, Sclerotium rolfsii, Spicaria sp. Selenophoma leaf spot Selenophoma sp. Sheath rot Gaeumannomyces graminis Shuck rot Myrothecium gramineum Silage mold Monascus purpureus, M ruber Smut, common Ustilago zeae = U. maydis Smut, false Ustilaginoidea virens Smut, head Sphacelotheca reiliana = Sporisorium holcisorghi Southern corn leaf Cochliobolus heterostrophus (anamorph: blight and stalk rot Bipolaris maydis = Helminthosporium maydis) Southern leaf spot Stenocarpella macrospora = Diplodia macrospora Stalk rots, minor Cercospora sorghi, Fusarium episphaeria, F. merismoides, F. oxysporum Schlechtend, F. poae, F. roseum, F. solani (teleomorph: Nectria haematococca), F. tricinctum, Mariannaea elegans, Mucor sp., Rhopographus zeae, Spicaria sp. Storage rots Aspergillus spp., Penicillium spp. and other fungi Tar spot Phyllachora maydis Trichoderma ear rot and Trichoderma viride = T. lignorum root rot teleomorph: Hypocrea sp. White ear rot, root and Stenocarpella maydis = Diplodia zeae stalk rot Yellow leaf blight Ascochyta ischaemi, Phyllosticta maydis (teleomorph: Mycosphaerella zeae-maydis) Zonate leaf spot Gloeocercospora sorghi

The following are especially preferred:

-   -   Plasmodiophoromycota such as Plasmodiophora brassicae (clubroot         of crucifers), Spongospora subterranea (powdery scab of potato         tubers), Polymyxa graminis (root disease of cereals and         grasses),     -   Oomycota such as Bremia lactucae (downy mildew of lettuce),         Peronospora (downy mildew) in snapdragon (P. antirrhini), onion         (P. destructor), spinach (P. effusa), soybean (P. manchurica),         tobacco (“blue-mold”; P. tabacina) alfalfa and clover (P.         trifolium), Pseudoperonospora humuli (downy mildew of hops),         Plasmopara (downy mildew in grapevines) (P. viticola) and         sunflower (P. halstedii), Sclerophtohra macrospora (downy mildew         in cereals and grasses), Pythium (seed rot, seedling         damping-off, and root rot and all types of plants, for example         damping-off of Beta beet caused by P. debaryanum), Phytophthora         infestans (blight in potato, brown rot in tomato and the like),         Albugo spec. (white rust on cruciferous plants).     -   Ascomycota such as Microdochium nivale (snow mold of rye and         wheat), Fusarium graminearum, Fusarium culmorum (partial ear         sterility mainly in wheat), Fusarium oxysporum (Fusarium wilt of         tomato), Blumeria graminis (powdery mildew of barley (f.sp.         hordei) and wheat (f.sp. tritici)), Erysiphe pisi (powdery         mildew of pea), Nectria galligena (Nectria canker of fruit         trees), Unicnula necator (powdery mildew of grapevine),         Pseudopeziza tracheiphila (red fire disease of grapevine),         Claviceps purpurea (ergot on, for example, rye and grasses),         Gaeumannomyces graminis (take-all on wheat, rye and other         grasses), Magnaporthe grisea (rice blast disease), Pyrenophora         graminea (leaf stripe of barley), Pyrenophora teres (net blotch         of barley), Pyrenophora tritici-repentis (leaf blight of wheat),         Venturia inaequalis (apple scab), Sclerotinia sclerotium (stalk         break, stem rot), Pseudopeziza medicaginis (leaf spot of         alfalfa, white and red clover).     -   Basidiomycetes such as Typhula incarnata (typhula blight on         barley, rye, wheat), Ustilago maydis (blister smut on maize),         Ustilago nuda (loose smut on barley), Ustilago tritici (loose         smut on wheat, spelt), Ustilago avenae (loose smut on oats),         Rhizoctonia solani (rhizoctonia root rot of potato),         Sphacelotheca spp. (head smut of sorghum), Melampsora lini (rust         of flax), Puccinia graminis (stem rust of wheat, barley, rye,         oats), Puccinia recondita (leaf rust on wheat), Puccinia         dispersa (brown rust on rye), Puccinia hordei (leaf rust of         barley), Puccinia coronata (crown rust of oats), Puccinia         striiformis(yellow rust of wheat, barley, rye and a large number         of grasses), Uromyces appendiculatus (brown rust of bean),         Sclerotium rolfsii (root and stem rots of many plants).     -   Deuteromycetes (Fungi imperfecti) such as Septoria nodorum         (glume blotch) of wheat (Septoria tritici), Pseudocercosporella         herpotrichoides (eyespot of wheat, barley, rye), Rynchosporium         secalis (leaf spot on rye and barley), Alternaria solani (early         blight of potato, tomato), Phoma betae (blackleg on Beta beet),         Cercospora beticola (leaf spot on Beta beet), Alternaria         brassicae (black spot on oilseed rape, cabbage and other         crucifers), Verticillium dahliae (verticillium wilt),         Colletotrichum lindemuthianum (bean anthracnose), Phoma lingam         (blackleg of cabbage and oilseed rape), Botrytis cinerea (grey         mold of grapevine, strawberry, tomato, hops and the like).

Most preferred are Phytophthora infestans (potato blight, brown rot in tomato and the like), Microdochium nivale (previously Fusarium nivale; snow mold of rye and wheat), Fusarium graminearum, Fusarium culmorum (partial ear sterility of wheat), Fusarium oxysporum (Fusarium wilt of tomato), Blumeria graminis (powdery mildew of barley (f. sp. hordei) and wheat (f. sp. tritici)), Magnaporthe grisea (rice blast disease), Sclerotinia sclerotium (stalk break, stem rot), Septoria nodorum and Septoria tritici (glume blotch of wheat), Alternaria brassicae (black spot of oilseed rape, cabbage and other crucifers), Phoma lingam (blackleg of cabbage and oilseed rape).

-   2. Bacterial pathogens:

The pathogens and the diseases associated with them which are mentioned in Table 3 may be mentioned by way of example but not by limitation. TABLE 3 Bacterial diseases Disease Pathogen Bacterial leaf blight and Pseudomonas avenae subsp. avenae stalk rot Bacterial leaf spot Xanthomonas campestris pv. holcicola Bacterial stalk rot Enterobacter dissolvens = Erwinia dissolvens Bacterial stalk and top Erwinia carotovora subsp. rot carotovora, Erwinia chrysanthemi pv. zeae Bacterial stripe Pseudomonas andropogonis Chocolate spot Pseudomonas syringae pv. coronafaciens Goss's bacterial wilt and Clavibacter michiganensis subsp. blight (leaf freckles and nebraskensis = Corynebacterium wilt) michiganense pv. andnebraskense Holcus spot Pseudomonas syringae pv. syringae Purple leaf sheath Hemiparasitic bacteria Seed rot-seedling blight Bacillus subtilis Stewart's disease Pantoea stewartii = Erwinia (bacterial wilt) stewartii Corn stunt Spiroplasma kunkelii (achapparramiento, maize stunt, Mesa Central or Rio Grande maize stunt)

The following pathogenic bacteria are very especially preferred: Corynebacterium sepedonicum (bacterial ring rot of potato), Erwinia carotovora (black leg of potato), Erwinia amylovora (fire blight of pear, apple, quince), Streptomyces scabies (potato scab), Pseudomonas syringae pv. tabaci (wildfire of tobacco), Pseudomonas syringae pv. phaseolicola (grease spot of dwarf bean), Pseudomonas syringae pv. tomato (bacterial speck of tomato), Xanthomonas campestris pv. malvacearum (bacterial blight of cotton) and Xanthomonas campestris pv. oryzae (bacterial leaf blight of rice and other grasses).

-   3. Viral Pathogens:     -   “Viral pathogens” includes all plant viruses such as, for         example, tobacco or cucumber mosaic virus, ringspot virus,         necrosis virus, maize dwarf mosaic virus and the like.

The pathogens and diseases associated with them which are mentioned in Table 4 may be mentioned by way of example, but not by limitation. TABLE 4 Viral diseases Disease Pathogen American wheat striate American wheat striate mosaic virus (wheat striate mosaic) (AWSMV) Barley stripe mosaic Barley stripe mosaic virus (BSMV) Barley yellow dwarf Barley yellow dwarf virus (BYDV) Brome mosaic Brome mosaic virus (BMV) Cereal chlorotic mottle Cereal chlorotic mottle virus (CCMV) Corn chlorotic vein Corn chlorotic vein banding virus banding (Brazilian maize (CCVBV) mosaic) Corn lethal necrosis Virus complex of Maize chlorotic mottle virus (MCMV) and Maize dwarf mosaic virus (MDMV) A or B or Wheat streak mosaic virus(WSMV) Cucumber mosaic Cucumber mosaic virus (CMV) Cynodon chlorotic streak Cynodon chlorotic streak virus (CCSV) Johnsongrass mosaic Johnsongrass mosaic virus (JGMV) Maize bushy stunt Mycoplasma-like organism (MLO) associated Maize chlorotic dwarf Maize chlorotic dwarf virus (MCDV) Maize chlorotic mottle Maize chlorotic mottle virus (MCMV) Maize dwarf mosaic Maize dwarf mosaic virus (MDMV) strains A, D, E and F Maize leaf fleck Maize leaf fleck virus (MLFV) Maize line Maize line virus (MLV) Maize mosaic (corn leaf Maize mosaic virus (MMV) stripe, enanismo rayado) Maize mottle and Maize mottle and chlorotic stunt virus chlorotic stunt Maize pellucid ringspot Maize pellucid ringspot virus (MPRV) Maize raya gruesa Maize raya gruesa virus (MRGV) Maize rayado fino (fine Maize rayado fino virus (MRFV) striping disease) Maize red leaf and red Mollicute stripe Maize red stripe Maize red stripe virus (MRSV) Maize ring mottle Maize ring mottle virus (MRMV) Maize rio IV Maize rio cuarto virus (MRCV) Maize rough dwarf Maize rough dwarf virus (MRDV) (Cereal (nanismo ruvido) tillering disease virus) Maize sterile stunt Maize sterile stunt virus (strains of barley yellow striate virus) Maize streak Maize streak virus (MSV) Maize stripe (maize Maize stripe virus chlorotic stripe, maize hoja blanca) Maize stunting Maize stunting virus Maize tassel abortion Maize tassel abortion virus (MTAV) Maize vein enation Maize vein enation virus (MVEV) Maize wallaby ear Maize wallaby ear virus (MWEV) Maize white leaf Maize white leaf virus Maize white line mosaic Maize white line mosaic virus (MWLMV) Millet red leaf Millet red leaf virus (MRLV) Northern cereal mosaic Northern cereal mosaic virus (NCMV) Oat pseudorosette Oat pseudorosette virus (zakuklivanie) Oat sterile dwarf Oat sterile dwarf virus (OSDV) Rice black-streaked Rice black-streaked dwarf virus dwarf (RBSDV) Rice stripe Rice stripe virus (RSV) Sorghum mosaic Sorghum mosaic virus (SrMV) (auch: sugarcane mosaic virus (SCMV) Stamme H, I and M) Sugarcane Fiji disease Sugarcane Fiji disease virus (FDV) Sugarcane mosaic Sugarcane mosaic virus (SCMV) strains A, B, D, E, SC, BC, Sabi and MB (formerly MDMV-B) Wheat spot mosaic Wheat spot mosaic virus (WSMV)

-   4. Animal Pests -   4.1 Insect Pathogens:     -   The following may be mentioned by way of example, but not by         limitation: insects such as, for example, beetles, caterpillars,         lice or mites. Preferred insects are those of the genera         Coleoptera, Diptera, Hymenoptera, Lepidoptera, Mallophaga,         Homoptera, Hemiptera, Orthoptera, Thysanoptera, Dermaptera,         Isoptera, Anoplura, Siphonaptera, Trichoptera, etc. Especially         preferred are coleopteran and lepidopteran insects such as, for         example, the European corn borer (ECB), Diabrotica barberi         (northern corn rootworm), Diabrotica undecimpunctata (southern         corn rootworm), Diabrotica virgifera (Western corn rootworm),         Agrotis ipsilon (black cutworm), Crymodes devastator (glassy         cutworm), Feltia ducens (dingy cutworm), Agrotis gladiaria         (claybacked cutworm), Melanotus spp., Aeolus mellillus         (wireworm), Aeolus mancus (wheat wireworm), Horistonotus uhlerii         (sand wireworm), Sphenophorus maidis (maize billbug),         Sphenophorus zeae (timothy billbug), Sphenophorus parvulus         (bluegrass billbug), Sphenophorus callosus (southern corn         billbug), Phyllogphaga spp. (white grubs), Anuraphis         maidiradicis (corn root aphid), Delia platura (seedcorn maggot),         Colaspis brunnea (grape colaspis), Stenolophus lecontei         (seedcorn beetle) and Clivinia impressifrons (lender seedcorn         beetle).     -   Other examples are: lema (Oulema melanopus), frit fly (Oscinella         frit), wireworms (Agrotis lineatus) and aphids (such as, for         example, the oat grain aphid Rhopalosiphum padi, the blackberry         aphid Sitobion avenae). -   4.2 Nematodes:

The pathogens and the diseases associated with them mentioned in Table 6 may be mentioned by way of example, but not by limitation. TABLE 6 Parasitic nematodes Damage Pathogenic nematode Awl Dolichodorus spp., D. heterocephalus Bulb and stem nematode Ditylenchus dipsaci disease; Europe Burrowing Radopholus similis Cyst nematode disease Heterodera avenae, H. zeae, Punctodera chalcoensis Dagger Xiphinema spp., X. americanum, X. mediterraneum False root-knot Nacobbus dorsalis Lance, Columbia Hoplolaimus columbus Lance Hoplolaimus spp., H. galeatus Lesion Pratylenchus spp., P. brachyurus, P. crenatus, P. hexincisus, P. neglectus, P. penetrans, P. scribneri, P. thornei, P. zeae Needle Longidorus spp., L. breviannulatus Ring Criconemella spp., C. ornata Root-knot disease Meloidogyne spp., M. chitwoodi, M. incognita, M. javanica Spiral Helicotylenchus spp. Sting Belonolaimus spp., B. longicaudatus Stubby-root Paratrichodorus spp., P. christiei, P. minor, Quinisulcius acutus, Trichodorus spp. Stunt Tylenchorhynchus dubius

Very especially preferred are Globodera rostochiensis and G. pallida (cyst eelworm on potato, tomato and other Solanaceae), Heterodera schachtii (beet eelworm on sugar and fodder beet, oilseed rape, cabbage and the like), Heterodera avenae (oat cyst nematode on oat and other cereal species), Ditylenchus dipsaci (stem or bulb eelworm, stem eelworm of rye, oats, maize, clover, tobacco, beet), Anguina tritici (grain nematode, cockle disease of wheat (spelt, rye), Meloidogyne hapla (root-knot nematode of carrot, cucumber, lettuce, tomato, potato, sugar beet, lucerne).

Examples of preferred fungal or viral pathogens for the individual varieties are:

-   1. Barley:     -   Fungal, bacterial and viral pathogens: Puccinia graminis f.sp.         hordei (barley stem rust), Blumeria (Erysiphe) graminis f.sp.         hordei (barley powdery mildew), barley yellow dwarf virus         (BYDV),     -   Pathogenic insects/nematodes: Ostrinia nubilalis (European corn         borer); Agrotis ipsilon (black cutworm); Schizaphis graminum         (greenbug); Blissus leucopterus leucopterus (chinch bug);         Acrosternum hilare (green stink bug); Euschistus servus (brown         stink bug); Deliaplatura (seedcorn maggot); Mayetiola destructor         (Hessian fly); Petrobia latens (brown wheat mite). -   2. Soybean:     -   Fungal, bacterial or viral pathogens: Phytophthora megasperma         fsp. glycinea, Macrophomina phaseolina, Rhizoctonia solani,         Sclerotinia sclerotiorum, Fusarium oxysporum, Diaporthe         phaseolorum var. sojae (Phomopsis sojae), Diaporthe phaseolorum         var. caulivora, Sclerotium rolfsii, Cercospora kikuchii,         Cercospora sojina, Peronospora manshurica, Colletotrichum         dematium (Colletotrichum truncatum), Corynespora cassiicola,         Septoria glycines, Phyllosticta sojicola, Alternaria alternata,         Pseudomonas syringae p.v. glycinea, Xanthomonas campestris p.v.         phaseoli, Microsphaera diffussa, Fusarium semitectum,         Phialophora gregata, soybean mosaic virus, Glomerella glycines,         Tobacco Ring spot virus, Tobacco Streak virus,         Phakopsorapachyrhizi, Pythium aphanidermatum, Pythium ultimum,         Pythium debaryanum, Tomato spotted wilt virus, Heterodera         glycines Fusarium solani.     -   Pathogenic insects/nematodes: Pseudoplusia includens (soybean         looper); Anticarsia gemmatalis (velvetbean caterpillar);         Plathypena scabra (green cloverworm); Ostrinia nubilalis         (European corn borer); Agrotis ipsilon (black cutworm);         Spodoptera exigua (beet armyworm); Heliothis virescens (cotton         budworm); Helicoverpa zea (cotton bollworm); Epilachna         varivestis (Mexican bean beetle); Myzus persicae (green peach         aphid); Empoasca fabae (potato leaf hopper); Acrosternum hilare         (green stink bug); Melanoplus femurrubrum (redlegged         grasshopper); Melanoplus differentialis (differential         grasshopper); Hylemya platura (seedcom maggot); Sericothrips         variabilis (soybean thrips); Thrips tabaci (onion thrips);         Tetranychus turkestani (strawberry spider mite); Tetranychus         urticae (two-spotted spider mite). -   3. Canola:     -   Fungal, bacterial or viral pathogens: Albugo candida, Alternaria         brassicae, Leptosphaeria maculans, Rhizoctonia solani,         Sclerotinia sclerotiorum, Mycosphaerella brassiccola, Pythium         ultimum, Peronospora parasitica, Fusarium roseum, Alternaria         alternata. -   4. Alfalfa:     -   Fungal, bacterial or viral pathogens: Clavibater michiganese         subsp. insidiosum, Pythium ultimum, Pythium irregulare, Pythium         splendens, Pythium debaryanum, Pythium aphanidermatum,         Phytophthora megasperma, Peronospora trifoliorum, Phoma         medicaginis var. medicaginis, Cercospora medicaginis,         Pseudopeziza medicaginis, Leptotrochila medicaginis, Fusarium,         Xanthomonas campestris p.v. alfalfae, Aphanomyces euteiches,         Stemphylium herbarum, Stemphylium alfalfae. -   5. Wheat:     -   Fungal, bacterial or viral pathogens: Pseudomonas syringae p.v.         atrofaciens, Urocystis agropyri, Xanthomonas campestris p.v.         translucens, Pseudomonas syringae p.v. syringae, Alternaria         alternata, Cladosporium herbarum, Fusarium graminearum, Fusarium         avenaceum, Fusarium culmorum, Ustilago tritici, Ascochyta         tritici, Cephalosporium gramineum, Collotetrichum graminicola,         Erysiphe graminis f.sp. tritici, Puccinia graminis f.sp.         tritici, Puccinia recondita f.sp. tritici, Puccinia striiformis,         Pyrenophora tritici-repentis, Septoria nodorum, Septoria         tritici, Septoria avenae, Pseudocercosporella herpotrichoides,         Rhizoctonia solani, Rhizoctonia cerealis, Gaeumannomyces         graminis var. tritici; Pythium aphanidermatum, Pythium         arrhenomanes, Pythium ultimum, Bipolaris sorokiniana, Barley         Yellow Dwarf Virus, Brome Mosaic Virus, soil borne wheat mosaic         virus, wheat streak mosaic virus, wheat spindle streak virus,         American wheat striate virus, Claviceps purpurea, Tilletia         tritici, Tilletia laevis, Ustilago tritici, Tilletia indica,         Rhizoctonia solani, Pythium arrhenomannes, Pythium gramicola,         Pythium aphanidermatum, high plains virus, European wheat         striate virus, Puccinia graminis f.sp. tritici (wheat stem         rust), Blumeria (Erysiphe) graminis f.sp. tritici (wheat powdery         mildew).     -   Pathogenic insects/nematodes: Pseudaletia unipunctata         (armyworm); Spodoptera, frugiperda (fall armyworm); Elasmopalpus         lignosellus (lesser cornstalk borer); Agrotis orthogonia         (western cutworm); Elasmopalpus Zignosellus (lesser cornstalk         borer); Oulema melanopus (cereal leaf beetle); Hypera punctata         (clover leaf weevil); Diabrotica undecimpunctata howardi         (southern corn rootworm); Russian wheat aphid; Schizaphis         graminum (greenbug); Macrosiphum avenae (English grain aphid);         Melanoplus femurrubrum (redlegged grasshopper); Melanoplus         differentialis (differential grasshopper); Melanoplus         sanguinipes (migratory grasshopper); Mayetiola destructor         (Hessian fly); Sitodiplosis mosellana (wheat midge); Meromyza         americana (wheat stem maggot); Hylemya coarctata (wheat bulb         fly); Frankliniella fusca (tobacco thrips); Cephus cinctus         (wheat stem sawfly); Aceria tulipae (wheat curl mite). -   6. Sunflower:     -   Fungal, bacterial or viral pathogens: Plasmophora halstedii,         Sclerotinia sclerotiorum, aster yellows, Septoria helianthi,         Phomopsis helianthi, Alternaria helianthi, Alternaria zinniae,         Botrytis cinerea, Phoma macdonaldii, Macrophomina phaseolina,         Erysiphe cichoracearum, Rhizopus oryzae, Rhizopus arrhizus,         Rhizopus stolonifer, Puccinia helianthi, Verticillium dahliae,         Erwinia carotovorum p.v. Carotovora, Cephalosporium acremonium,         Phytophthora cryptogea, Albugo tragopogonis.     -   Pathogenic insects/nematodes: Suleima helianthana (sunflower bud         moth); Homoeosoma electellum (sunflower moth); zygogramma         exclamationis (sunflower beetle); Bothyrus gibbosus (carrot         beetle); Neolasioptera murtfeldtiana (sunflower seed midge). -   7. Maize:     -   Fungal, bacterial or viral pathogens: Fusarium moniliforme var.         subglutinans, Erwinia stewartii, Fusarium moniliforme,         Gibberella zeae (Fusarium graminearum), Stenocarpella maydi         (Diplodia maydis), Pythium irregulare, Pythium debaryanum,         Pythium graminicola, Pythium splendens, Pythium ultimum, Pythium         aphanidermatum, Aspergillus flavus, Bipolaris maydis 0, T         (Cochliobolus heterostrophus), Helminthosporium carbonum I, II &         III (Cochliobolus carbonum), Exserohilum turcicum I, II & III,         Helminthosporium pedicellatum, Physoderma maydis, Phyllosticta         maydis, Kabatiella maydis, Cercospora sorghi, Ustilago maydis,         Puccinia sorghi, Puccinia polysora, Macrophomina phaseolina,         Penicillium oxalicum, Nigrospora oryzae, Cladosporium herbarum,         Curvularia lunata, Curvularia inaequalis, Curvularia pallescens,         Clavibacter michiganese subsp. nebraskense, Trichoderma viride,         maize dwarf mosaic virus A & B, wheat streak mosaic virus, maize         chlorotic dwarf virus, Claviceps sorghi, Pseudonomas avenae,         Erwinia chrysanthemi p.v. Zea, Erwinia corotovora, cornstunt         spiroplasma, Diplodia macrospora, Sclerophthora macrospora,         Peronosclerospora sorghi, Peronosclerospora philippinesis,         Peronosclerospora maydis, Peronosclerospora sacchari,         Spacelotheca reiliana, Physopella zeae, Cephalosporium maydis,         Caphalosporium acremonium, maize chlorotic mottle virus, high         plains virus, maize mosaic virus, maize rayado fino virus, maize         streak virus (MSV), maize stripe virus, maize rough dwarf virus.     -   Pathogenic insects/nematodes: Ostrinia nubilalis (European corn         borer); Agrotis ipsilon (black cutworm); Helicoverpa zea (corn         earworm); Spodoptera frugiperda (fall armyworm); Diatraea         grandiosella (Southwestern corn borer); Elasmopalpus lignosellus         (lesser cornstalk borer); Diatraea saccharalis (surgarcane         borer); Diabrotica virgifera (Western corn rootworm); Diabrotica         longicornis barberi (Northern corn rootworm); Diabrotica         undecimpunctata howardi (Southern corn rootworm); Melanotus spp.         (wireworms); Cyclocephala borealis (Northern masked chafer;         white grub); Cyclocephala immaculata (Southern masked chafer;         white grub); Popillia japonica (Japanese beetle); Chaetocnema         pulicaria (corn flea beetle); Sphenophorus maidis (maize         billbug); Rhopalosiphum maidis (corn leaf aphid); Anuraphis         maidiradicis (corn root aphid); Blissus leucopterus leucopterus         (chinch bug); Melanoplus femur-rubrum (red-legged grasshopper);         Melanoplus sanguinipes (migratory grasshopper); Hylemva platura         (seedcom maggot); Agromyza parvicornis (corn blot leafminer);         Anaphothrips obscrurus (grass thrips); Solenopsis milesta (thief         ant); Tetranychus urticae (two-spotted spider mite). -   8. Sorghum:     -   Fungal, bacterial or viral pathogens: Exserohilum turcicum,         Colletotrichum graminicola (Glomerella graminicola), Cercospora         sorghi, Gloeocercospora sorghi, Ascochyta sorghina, Pseudomonas         syringae p.v. syringae, Xanthomonas campestris p.v. holcicola,         Pseudomonas andropogonis, Puccinia purpurea, Macrophomina         phaseolina, Perconia circinata, Fusarium moniliforme, Alternaria         alternate, Bipolaris sorghicola, Helminthosporium sorghicola,         Curvularia lunata, Phoma insidiosa, Pseudomonas avenae         (Pseudomonas alboprecipitans), Ramulispora sorghi, Ramulispora         sorghicola, Phyllachara sacchari, Sporisorium reilianum         (Sphacelotheca reiliana), Sphacelotheca cruenta, Sporisorium         sorghi, sugarcane mosaic H, maize dwarf mosaic virus A & B,         Claviceps sorghi, Rhizoctonia solani, Acremonium strictum,         Sclerophthona macrospora, Peronosclerospora sorghi,         Peronosclerospora philippinensis, Sclerospora graminicola,         Fusarium graminearum, Fusarium oxysporum, Pythium arrhenomanes,         Pythium graminicola.     -   Pathogenic insects/nematodes: Chilo partellus (sorghum borer);         Spodoptera frugiperda (fall armyworm); Helicoverpa zea (corn         ear-worm); Elasmopalpus lignosellus (lesser cornstalk borer);         Feltia subterranea (granulate cutworm); Phvllophaga crinita         (white grub); Eleodes, Conoderus and Aeolus spp. (wireworm);         Oulema melanopus (cereal leaf beetle); Chaetocnema pulicaria         (corn flea beetle); Sphenophorus maidis (maize billbug);         Rhopalosiphum maidis (corn leaf aphid); Siphaflava (yellow         sugarcane aphid); Blissus leucopterus leucopterus (chinch bug);         Contarinia sorghicola (sorghum midge); Tetranychus cinnabarinus         (carmine spider mite); Tetranychus urticae (two-spotted spider         mite). -   9. Cotton:     -   Pathogenic insects/nematodes: Heliothis virescens (cotton         budworm); Helicoverpa zea (cotton bollworm); Spodoptera exigua         (beet armyworm); Pectinophora gossypiella (pink bollworm);         Anthonomus grandis grandis (boll weevil); Aphis gossypii (cotton         aphid); Pseudatomoscelis seriatus (cotton fleahopper);         Trialeurodes abutilonea (banded-winged whitefly); Lygus         lineolaris (tarnished plant bug); Melanoplus femurrubrum         (red-legged grasshopper); Melanoplus differentialis         (differential grasshopper); Thrips tabaci (onion thrips);         Franklinkiella fusca (tobacco thrips); Tetranychus cinnabarinus         (carmine spider mite); Tetranychus urticae (two-spotted spider         mite). -   10. Rice:     -   Pathogenic insects/nematodes: Diatraea saccharalis (sugarcane         borer); Spodoptera frugiperda (fall armyworm); Helicoverpa zea         (corn earworm); Colaspis brunnea (grape colaspis); Lissorhoptrus         oryzophilus (rice water weevil); Sitophilus oryzae (rice         weevil); Nephotettix nigropictus (rice leafhopper); Blissus         Ieucopterus leucopterus (chinch bug); Acrosternum hilare (green         stink bug). -   11. Oilseed rape:     -   Pathogenic insects/nematodes: Brevicoryne brassicae (cabbage         aphid); Phyilotreta cruciferae (flea beetle); Mamestra         conjgurata (bertha armyworm); Plutella xylostella (diamond-back         moth); Delia ssp. (root maggots).

For the purposes of the invention, “RacB protein” is understood as meaning the RacB protein from barley as shown in SEQ ID NO: 2, and its homologs from rice (Oryza sative) as shown in SEQ ID NO: 4 and maize (Zea mays) as shown in SEQ ID NO: 6, and functional equivalents of the above-mentioned.

“Amount of protein” is understood as meaning the amount of an RacB polypeptide in an organism, a tissue, a cell or a cell compartment. “Reduction” of the amount of protein means the quantitative reduction of the amount of an RacB protein in an organism, a tissue, a cell or a cell compartment—for example by one of the methods described hereinbelow—in comparison with the wild type of the same genus and species, to which this method had not been applied, under otherwise identical conditions (such as, for example, culture conditions, plant age and the like). The reduction amounts to at least 10%, preferably at least 10% or at least 20%, especially preferably at least 40% or 60%, very especially preferably at least 70% or 80%, most preferably at least 90% or 95%.

“Activity” is preferably understood as meaning the GTPase activity of an RacB polypeptide in an organism, a tissue, a cell or a cell compartment. “Reduction” of the activity is understood as meaning the reduction of the total activity of an RacB protein in an organism, a tissue, a cell or a cell compartment—for example by one of the methods described hereinbelow—in comparison with the wild type of the same genus and species, to which this method had not been applied, under otherwise identical conditions (such as, for example, culture conditions, plant age and the like). The reduction amounts to at least 10%, preferably at least 10% or at least 20%, especially preferably at least 40% or 60%, very especially preferably at least 70% or 80%, most preferably at least 90% or 95%.

“Function” is preferably understood as meaning the substrate-binding capacity of an RacB polypeptide in an organism, a tissue, a cell or a cell compartment. Suitable substrates are low-molecular-weight compounds such as GTP, but also the protein interaction partners of an RacB protein. “Reduction” of the function is understood as meaning, for example, the quantitative reduction of the binding capacity or binding strength of an RacB protein to at least one substrate in an organism, a tissue, a cell or a cell compartment—for example by one of the methods described hereinbelow—in comparison with the wild type of the same genus and species, to which this method had not been applied, under otherwise identical conditions (such as, for example, culture conditions, plant age and the like). Reduction is also understood as meaning the change in substrate specificity as can be expressed for example by the kcat/Km value. The reduction amounts to at least 10%, preferably at least 10% or at least 20%, especially preferably at least 40% or 60%, very especially preferably at least 70% or 80%, most preferably at least 90% or 95%. Binding partners for RacB can be identified in a manner with which the skilled worker is familiar, for example by the yeast-2-hybrid system.

Methods of determining the amount of protein, the activity of GTPases or the substrate binding capacity are known to the skilled worker and have been described on a number of occasions for GTPases and for Rac proteins from a variety of genera and species (see, inter alia, Benard V et al. (1999) J Biol Chem 274(19):13198-204; Burstein E S (1998) Oncogene. 17(12):1617-23).

“Functional equivalents” of an RacB protein is preferably understood as meaning those sequences which are derived from, or are homologous to, an RacB protein described by SEQ ID NO: 2, 4 or 6 and which have essentially the same properties.

“Essentially the same properties” of a functional equivalent is above all understood as meaning conferring a pathogen-resistant phenotype or conferring or increasing the resistance to at least one pathogen while reducing the amount of protein, activity or function of said functional RacB equivalent in a plant or in a tissue, part or cells of the same. The absence of a spontaneously induced cell death in combination with said reduction of the amount of protein, activity or function of the functional equivalent is furthermore understood as an essential property.

In this context, the efficacy of the pathogen resistance can deviate both downward or upward in comparison with a value obtained when reducing one of the RacB proteins as shown in SEQ ID NO: 2, 4 or 6. Preferred functional equivalents are those in which the efficacy of the pathogen resistance—measured, for example, by the penetration efficacy of a pathogen (formation of haustoria)—differs by not more than 50%, preferably 25%, especially preferably 10% from a comparative value obtained by reducing an RacB protein as shown in NO: 2, 4 or 6. Especially preferred are those sequences where the reduction increases the efficacy of pathogen resistance quantitatively by more than 50%, preferably 100%, especially preferably 500%, very especially preferably 1000% based on a comparative value obtained by reducing one of the RacB protein as shown in SEQ ID NO: 2, 4 or 6.

The comparison is preferably carried out under analogous conditions. “Analogous conditions” means that all conditions such as, for example, culture or growing conditions, assay conditions (such as buffer, temperature, substrates, pathogen concentration and the like) are kept identical between the experiments to be compared and that the set-ups differ only by the sequence of the RacB polypeptides to be compared, their organism of origin and, if appropriate, the pathogen. When choosing the pathogen, each comparison requires that the pathogen be chosen which is most similar to the other equivalent, taking into consideration the species specificity.

“Functional equivalents” is understood as meaning, in particular, natural or artificial mutations of the RacB polypeptides as shown in SEQ ID NO: 2, 4 or 6 and homologous polypeptides from other plants which continue to have essentially the same properties. Homologous polypeptides from the above-described preferred plants are preferred. The sequences from other plants (for example Arabidopsis thaliana) which are homologous to the RacB sequences disclosed within the scope of the present invention can be found readily for example by database search or by screening genetic libraries using the RacB sequences as search sequence or probe.

Mutations comprise substitutions, additions, deletions, inversion or insertions of one or more amino acid residues. Thus, the present invention also comprises those polypeptides which are obtained by modification of a polypeptide as shown in SEQ ID NO: 2, 4 or 6.

Homology between two nucleic acid sequences is understood as meaning the identity of the nucleic acid sequence over in each case the entire sequence length which is calculated by comparison with the aid of the program algorithm GAP (Wisconsin Package Version 10.0, University of Wisconsin, Genetics Computer Group (GCG), Madison, USA; Altschul et al. (1997) Nucleic Acids Res. 25:3389 et seq.), setting the following parameters:

-   -   Gap weight: 50 Length weight: 3     -   Average match: 10 Average mismatch: 0

For example a sequence which has at least 80% homology with sequence SEQ ID NO: 1 at the nucleic acid level is understood as meaning a sequence which, upon comparison with the sequence SEQ ID NO: 1 by the above program algorithm with the above parameter set, has at least 80% homology.

Homology between two polypeptides is understood as meaning the identity of the amino acid sequence over in each case the entire sequence length which is calculated by comparison with the aid of the program algorithm GAP (Wisconsin Package Version 10.0, University of Wisconsin, Genetics Computer Group (GCG), Madison, USA), setting the following parameters:

-   -   Gap weight: 8 Length weight: 2     -   Average match: 2,912 Average mismatch: −2,003

For example a sequence which has at least 80% homology with sequence SEQ ID NO: 2 at the protein level is understood as meaning a sequence which, upon comparison with the sequence SEQ ID NO: 2 by the above program algorithm with the above parameter set, has at least 80% homology.

Functional equivalents derived from one of the polypeptide as shown in SEQ ID NO: 2, 4 or 6 according to the invention by substitution, insertion or deletion have at least 60%, preferably at least 80%, by preference at least 90%, especially preferably at least 95%, very especially preferably at least 98%, homology with one of the polypeptide as shown in SEQ ID NO: 2, 4 or 6 according to the invention and are distinguished by essentially the same properties as the polypeptide as shown in SEQ ID NO: 2, 4 or 6.

Functional equivalents derived from the nucleic acid sequence as shown in SEQ ID NO: 1, 3 or 5 according to the invention by substitution, insertion or deletion have at least 60%, preferably at least 80%, by preference at least 90%, especially preferably at least 95%, very especially preferably at least 98%, homology with one of the polypeptides as shown in SEQ ID NO: 1, 3 or 5 according to the invention and encode polypeptides having essentially the same properties as the polypeptide as shown in SEQ ID NO: 2, 4 or 6.

The RacB proteins comprised as functional equivalents preferably have at least one of the following sequence motifs:

-   a) A G1 element GXXXXGKS/T preferably in the N-terminal region, very     especially preferably an element with the sequence GDGAVGKT, most     preferably an element with the sequence KCVTVGDGAVGKTC. -   b) A G2 effector region comprising a sequence motif with PTVFDN,     especially preferably NTFPTDYVPTVFDNFSANVV. -   c) A G3 element comprising LWDTAGQ, especially preferably     NLGLWDTAGQEDYN. -   d) A G4 element TKXD, especially preferably TKLD, very especially     preferably LVGTKLDLRDDKQ. -   e) A G5 element EXS, preferably ECSS, very especially preferably     ECSSKTG. -   f) A C-terminal isoprenylation motif (CXXX, Hassanain H H et     al. (2000) Biochem Biophys Res Commun. 272(3):783-8.), especially     preferably CSIL.

Especially preferably, at least 2 or 3 of these motifs (a to f) occur in a functionally equivalent RacB protein, very especially preferably at least 4 or 5 of these motifs, most preferably all motifs a to f. Further sequence motifs which are typical for RacB, in particular also motifs which constitute a delimitation against Rac1 proteins, can be deduced readily by the skilled worker from the sequence alignment of the known RacB (or Rac1) proteins, as shown in FIG. 1.

Examples of the functional equivalents to the RacB proteins as shown in SEQ ID NO: 2, 4 or 6, which equivalents are to be reduced in the method according to the invention, can be identified for example from a variety of organisms whose genomic sequence is known, such as, for example, from Arabidopsis thaliana, Brassica napus, Nicotiana tabacum, Solanum tuberosum, or Helianthinum from databases of homology comparisons.

The screening of cDNA libraries or genomic libraries of other organisms, preferably of the plant species which are mentioned further below as hosts for the transformation, using the nucleic acid sequences described under SEQ ID NO: 1, 3 or 5 or parts of these as probe is also a method of identifying homologs in other species with which the skilled worker is familiar. In this context, the probes derived from the nucleic acid sequences as shown in SEQ ID NO: 1, 3 or 5 have a length of at least 20 bp, preferably 50 bp, particularly preferably 100 bp, very especially preferably 200 bp, and most preferably 400 bp. A DNA strand which is complementary to the sequences described under SEQ ID NO: 1, 3 or 5 may also be employed for screening the libraries.

Functional equivalents, accordingly, comprise DNA sequences which hybridize under standard conditions with the RacB nucleic acid sequence described by SEQ ID NO: 1, 3 or 5, with the sequence complementary thereto or parts of the abovementioned and which, as complete sequences, encode proteins which have the same properties as the proteins described under SEQ ID NO: 2, 4 or 6.

“Standard hybridization conditions” is to be understood in the broad sense and means stringent or else less stringent hybridization conditions. Such hybridization conditions are described, inter alia, by Sambrook J, Fritsch E F, Maniatis T et al., in Molecular Cloning (A Laboratory Manual), 2nd Edition, Cold Spring Harbor Laboratory Press, 1989, pages 9.31-9.57) or in Current Protocols in Molecular Biology, John Wiley & Sons, N.Y. (1989), 6.3.1-6.3.6.

For example, the conditions during the wash step can be selected from the range of conditions delimited by low-stringency conditions (approximately 2×SSC at 50° C.) and high-stringency conditions (approximately 0.2×SSC at 50° C., preferably at 65° C.): (20×SSC: 0.3M sodium citrate, 3 M NaCl, pH 7.0). In addition, the temperature during the wash step can be raised from low-stringency conditions at room temperature, approximately 22° C., to higher-stringency conditions at approximately 65° C. Both of the parameters salt concentration and temperature can be varied simultaneously, or else one of the two parameters can be kept constant while only the other is varied. Denaturants, for example formamide or SDS, may also be employed during the hybridization.

In the presence of 50% formamide, hybridization is preferably effected at 42° C. Some examples of conditions for hybridization and wash step are shown hereinbelow:

-   (1) Hybridization conditions be selected, for example, from the     following conditions:     -   a) 4×SSC at 65° C.,     -   b) 6×SSC at 45° C.,     -   c) 6×SSC, 100 μg/ml denatured fragmented fish sperm DNA at 68°         C.,     -   d) 6×SSC, 0.5% SDS, 100 μg/ml denatured salmon sperm DNA at 68°         C.,     -   e) 6×SSC, 0.5% SDS, 100 μg/ml denatured fragmented salmon sperm         DNA, 50% formamide at 42° C.,     -   f) 50% formamide, 4×SSC at 42° C., or     -   g) 50% (vol/vol) formamide, 0.1% bovine serum albumin, 0.1%         Ficoll, 0.1% polyvinylpyrrolidone, 50 mM sodium phosphate buffer         pH 6.5, 750 mM NaCl, 75 mM sodium citrates at 42° C., or     -   h) 2× or 4×SSC at 50° C. (low-stringency condition),     -   i) 30 to 40% formamide, 2× or 4×SSC at 42° C. (low-stringency         condition). -   (2) Wash steps can be selected, for example, from the following     conditions:     -   a) 0.015 M NaCl/0.0015 M sodium citrate/0.1% SDS at 50° C.     -   b) 0.1×SSC at 65° C.     -   c) 0.1×SSC, 0.5% SDS at 68° C.     -   d) 0.1×SSC, 0.5% SDS, 50% formamide, at 42° C.     -   e) 0.2×SSC, 0.1% SDS at 42° C.     -   f) 2×SSC at 65° C. (low-stringency condition).

Functional equivalents derived from a polypeptide as shown in SEQ ID NO: 2, 4 or 6 comprises in particular also the proteins having the SEQ ID NO: 35, 37, 39, 41, 43, 45, 47, 50, 52, 54, 56, 58, 60, 62, 64, 66, 68 or 70. “Functional equivalents” is to be understood as meaning, in particular, proteins encoded by a nucleic acid sequence having the SEQ ID NO: 34, 36, 38, 40, 42, 44, 46, 48, 49, 51, 53, 55, 57, 61, 63, 65, 67 or 69.

The reduction of the expression of an RacB protein, the RacB activity or the RacB function can be realized in many ways.

“Reduction” or “reducing” in connection with an RacB protein, an RacB activity or an RacB function is to be interpreted in the wide sense and comprises the partial or essentially complete inhibition or blocking of the functionality of an RacB protein in a plant or a part, tissue, organ, cells or seeds thereof, which inhibition or blocking is based on a variety of cytobiological mechanisms.

For the purposes of the invention, a reduction also comprises a quantitative reduction of an RacB protein down to the essential complete absence of the RacB protein (i.e. lacking detectability of RacB activity or RacB function, or lacking immunological detectability of the RacB protein). In this context, the expression of a particular RacB protein, or the RacB activity or RacB function, in a cell or an organism is preferably reduced by more than 50%, especially preferably by more than 80%, very especially preferably by more than 90%.

A variety of strategies for reducing the expression of an RacB protein, the RacB activity or RacB function are comprised in accordance with the invention. The skilled worker is aware of a series of different methods being available for influencing the expression of an RacB protein, the RacB activity or the RacB function in the desired manner.

A reduction of the RacB activity or the RacB function is preferably achieved by reduced expression of an endogenous RacB protein.

A reduction of the amount of RacB protein, the RacB activity or the RacB function can be effected using the following methods:

-   -   a) Introduction of a double-stranded RacB RNA nucleic acid         sequence (RacB dsRNA) or an expression cassette(s) ensuring the         expression thereof     -   b) Introduction of an RacB antisense nucleic acid sequences or         an expression cassette ensuring expression thereof comprised are         those methods in which the antisense nucleic acid sequence is         directed against an RacB gene (i.e. genomic DNA sequences) or an         RacB gene transcript (i.e. RNA sequences). α-Anomeric nucleic         acid sequences are also comprised     -   c) Introduction of an RacB antisense nucleic acid sequences in         combination with a ribozyme or an expression cassette ensuring         expression thereof     -   d) Introduction of RacB sense nucleic acid sequences for         inducing cosuppression or an expression cassette ensuring         expression thereof     -   e) Introduction of a nucleic acid sequence encoding         dominant-negative RacB protein or an expression cassette         ensuring expression thereof     -   f) Introduction of DNA- or protein-binding factors against RacB         genes, RacB RNAs or RacB proteins or an expression cassette         ensuring expression thereof     -   g) Introduction of viral nucleic acid sequences and expression         constructs causing RacB RNA degradation or an expression         cassette ensuring expression thereof     -   h) Introduction of constructs for inducing a homologous         recombination on endogenous RacB genes, for example for         generating knock-out mutants     -   i) Introduction of mutations into endogenous RacB genes for         generating a loss of function (for example generation of stop         codons, reading-frame shifts and the like).

In this context, each and every of these methods may bring about a reduction of the RacB expression, RacB activity or RacB function for the purposes of the invention. A combined use is also feasible. Further methods are known to the skilled worker and can comprise the hindering or prevention of RacB protein processing, of the RacB protein or RacB mRNA transport, inhibition of ribosome attachment, inhibition of RNA splicing, induction of an RacB-RNA-degrading enzyme and/or inhibition of translational elongation or termination.

The individual processes which are preferred may be described in greater detail hereinbelow:

-   a) Introduction of a Double-Stranded RacB RNA Nucleic Acid Sequence     (RacB dsRNA)

The method of regulating genes by means of double-stranded RNA (“double-stranded RNA interference”; dsRNAi) has been described repeatedly for animal and plant organisms (for example Matzke M A et al. (2000) Plant Mol Biol 43:401-415; Fire A. et al (1998) Nature 391:806-811; WO 99/32619; WO 99/53050; WO 00/68374; WO 00/44914; WO 00/44895; WO 00/49035; WO 00/63364). Express reference is made to the processes and methods described in the above references. Effective gene suppression can also be demonstrated upon transient expression or following transient transformation for example as the consequence of biolistic transformation (Schweizer P et al. (2000) Plant J 2000 24: 895-903). dsRNAi methods are based on the phenomenon that the simultaneous introduction of complementary strand and counterstrand of a gene transcript causes the expression of the gene in question to be suppressed in a highly efficient manner. The phenotype caused greatly resembles a corresponding knock-out mutant (Waterhouse P M et al. (1998) Proc Natl Acad Sci USA 95:13959-64).

The dsRNAi method has proved to be particularly effective and advantageous for reducing the RacB expression. As described, inter alia, in WO 99/32619, dsRNAi approaches are markedly superior to traditional antisense approaches.

The invention therefore furthermore relates to double-stranded RNA molecules (dsRNA molecules) which, upon introduction into a plant (or a cell, tissue, organ or seed derived therefrom), bring about the reduction of an RacB.

In the double-stranded RNA molecule for reducing the expression of an RacB protein,

-   -   a) one of the two RNA strands is essentially identical to at         least a portion of an RacB nucleic acid sequence, and     -   b) the corresponding other RNA strand is essentially identical         to at least a portion of the complementary strand of an RacB         nucleic acid sequence.

In a further preferred embodiment, the double-stranded RNA molecule for reducing the expression of an RacB protein comprises

-   -   a) a sense RNA strand comprising at least one ribonucleotide         sequence which is essentially identical to at least part of the         sense RNA transcript of a nucleic acid sequence encoding an RacB         protein, and     -   b) an antisense RNA strand which is essentially—preferably         completely—complementary to the RNA sense strand under a).

With respect to the double-stranded RNA molecules, RacB nucleic acid sequence is to be understood as meaning, preferably, a sequence as shown in SEQ ID NO: 1, 3 or 5 or a functional equivalent thereof as shown in SEQ ID NO: 34, 36, 38, 40, 42, 44, 46, 48, 49, 51, 53, 55, 57, 61, 63, 65, 67 or 69.

“Essentially identical” means that the dsRNA sequence can also show insertions, deletions or individual point mutations compared with the RacB target sequence or a functionally equivalent target sequence while still bringing about an effective reduction of the expression. The homology in accordance with the above definition preferably amounts to at least 75%, preferably at least 80%, very especially preferably at least 90%, most preferably 100%, between the sense strand of an inhibitory dsRNA and at least part of the sense RNA transcript of a nucleic acid sequence encoding an RacB protein or a functional equivalent thereof (or between the antisense strand of the complementary strand of a nucleic acid sequence encoding an RacB protein or a functional equivalent thereof).

The length of the part-segment amounts to at least 10 bases, preferably at least 25 bases, especially preferably at least 50 bases, very especially preferably at least 100 bases, most preferably at least 200 bases or at least 300 bases.

As an alternative, an “essentially identical” dsRNA can also be defined as a nucleic acid sequence which is capable of hybridizing with part of a storage protein gene transcript (for example in 400 mM NaCl, 40 mM PIPES pH 6.4, 1 mM EDTA at 50° C. or 70° C. for 12 to 16 h).

“Essentially complementary” is to be understood as meaning that the antisense RNA strand may also contain insertions, deletions and individual point mutations, compared to the complement of the sense RNA strand. Preferably, the homology between the antisense RNA strand and the complement of the sense RNA strand is at least 80%, preferably at least 90%, very particularly preferably at least 95%, most preferably 100%.

“Part of the sense RNA transcript” of a nucleic acid sequence encoding an RacB protein or a functional equivalent thereof is to be understood as meaning fragments of an RNA or mRNA transcribed from a nucleic acid sequence, preferably an RacB gene, encoding an RacB protein or a functional equivalent thereof. Here, the fragments preferably have a sequence length of at least 20 bases, preferably at least 50 bases, particularly preferably at least 100 bases, very particularly preferably at least 200 bases, most preferably at least 500 bases. Also comprised is the complete transcribed RNA or mRNA.

Also comprised is the use of the dsRNA molecules according to the invention in the methods according to the invention for generating a pathogen resistance in plants.

The dsRNA can be composed of one or more strands of polymerized ribonucleotides. Modifications both of the sugar-phosphate backbone and of the nucleosides may be present. For example, the phosphodiester bonds of the natural RNA can be modified in such a way that they comprise at least one nitrogen or sulfur hetero atom. Bases can be modified in such a way that the activity of, for example, adenosine deaminase is restricted. These and other modifications are described hereinbelow in the methods of stabilizing antisense RNA.

To achieve the same purpose, it is, of course, also possible to introduce a plurality of individual dsRNA molecules each comprising one of the ribonucleotide sequence sections defined above into the cell or the organism.

The dsRNA can be generated enzymatically or fully or partially synthesized chemically.

The double-stranded dsRNA structure can be formed starting from two complementary, separate RNA strands or, preferably, strands starting from an individual self-complementary RNA strand.

In a single self-complementary strand, sense and antisense sequence may be linked by a linking sequence (“linker”) and can form for example a hairpin structure. The linking sequence can preferably be an intron which is spliced out after the dsRNA has been synthesized.

The nucleic acid sequence encoding a dsRNA can comprise further elements such as, for example, transcription termination signals or polyadenylation signals.

If the two dsRNA strands are to be combined in a cell or plant, this can be effected in various ways:

-   -   a) transformation of the cell or plant with a vector comprising         both expression cassettes,     -   b) cotransformation of the cell or plant with two vectors, one         of them comprising the expression cassettes with the sense         strand and the other comprising the expression cassettes with         the antisense strand,     -   c) hybridizing two plants, each of which has been transformed         with one vector, one of the vectors comprising the expression         cassettes with the sense strand and the other comprising the         expression cassettes with the antisense strand.

The formation of the RNA duplex can be initiated either outside or within the cell. Like in WO 99/53050, the dsRNA can also comprise a hairpin structure by linking sense and antisense strand by means of a linker (for example an intron). The self-complementary dsRNA structures are preferred since they only require the expression of one construct and always comprise the complementary strands in an equimolar ratio.

The expression cassettes encoding the antisense or sense strand of a dsRNA or the self-complementary strand of the dsRNA are preferably inserted into a vector and, using the methods described hereinbelow, stably inserted into the genome of a plant in order to ensure permanent expression of the dsRNA, using selection markers for example.

The dsRNA can be introduced using a quantity which allows at least one copy per cell. Greater quantities (for example at least 5, 10, 100, 500 or 1000 copies per cell) may bring about a more effective reduction.

As already described, 100% sequence identity between dsRNA and an RacB gene transcript or the gene transcript of a functionally equivalent gene is not necessarily required in order to bring about an effective reduction of the RacB expression. Accordingly, there is the advantage that the method is tolerant with regard to sequence deviations as may exist as the consequence of genetic mutations, polymorphisms or evolutionary divergence. Thus, for example, it is possible to use the dsRNA generated on the basis of the RacB sequence of one organism to suppress the RacB expression in another organism. The high sequence homology between the RacB sequences from rice, maize and barley allows the conclusion that this protein is conserved to a high degree within plants, so that the expression of a dsRNA derived from one of the disclosed RacB sequences as shown in SEQ ID NO: 1, 3 or 5 appears to have an advantageous effect in other plant species as well.

Furthermore, owing to the high homology between the individual RacB proteins and their functional equivalents, it is possible using a single dsRNA generated from a certain RacB sequence of an organism to suppress the expression of further homologous RacB proteins and/or their functional equivalents of the same organism or else the expression of RacB proteins in other related species. For this purpose, the dsRNA preferably comprises sequence regions of RacB gene transcripts which correspond to conserved regions. Said conserved regions can easily be found by comparing sequences.

The dsRNA can be synthesized either in vivo or in vitro. To this end, a DNA sequence encoding a dsRNA can be brought into an expression cassette under the control of at least one genetic control element (such as, for example, promoter, enhancer, silencer, splice donor or splice acceptor or polyadenylation signal). Suitable advantageous constructions are described hereinbelow. Polyadenylation is not required, nor do elements for initiating translation have to be present.

A dsRNA can be synthesized chemically or enzymatically.

Cellular RNA polymerases or bacteriophage RNA polymerases (such as, for example, T3, T7 or SP6 RNA polymerase) can be used for this purpose. Suitable methods for expression of RNA in vitro are described (WO 97/32016; U.S. Pat. No. 5,593,874; U.S. Pat. No. 5,698,425, U.S. Pat. No. 5,712,135, U.S. Pat. No. 5,789,214, U.S. Pat. No. 5,804,693). A dsRNA which has been synthesized in vitro chemically or enzymatically can be isolated completely or to some degree from the reaction mixture, for example by extraction, precipitation, electrophoresis, chromatography or combinations of these methods, before being introduced into a cell, tissue or organism. The dsRNA can be introduced directly into the cell or else be applied extracellularly (for example into the interstitial space).

However, it is preferred to transform the plant stably with an expression construct which brings about the expression of the dsRNA. Suitable methods are described hereinbelow.

b) Introduction of an RacB Antisense Nucleic Acid Sequence

Methods for suppressing a specific protein by preventing its mRNA from accumulating by means of antisense technology have been described in many instances, including in the case of plants (Sheehy et al. (1988) Proc Natl Acad Sci USA 85: 8805-8809; U.S. Pat. No. 4,801,340; Mol JN et al. (1990) FEBS Lett 268(2):427-430). The antisense nucleic acid molecule hybridizes, or binds, with the cellular mRNA and/or genomic DNA encoding the RacB target protein to be suppressed. This suppresses the transcription and/or translation of the target protein. Hybridization can originate conventionally by the formation of a stable duplex or—in the case of genomic DNA—by the antisense nucleic acid molecule binding to the duplex of the genomic DNA by specific interaction in the major groove of the DNA helix.

An antisense nucleic acid sequence suitable for reducing an RacB protein can be deduced using the nucleic acid sequence encoding this protein, for example the nucleic acid sequence as shown in SEQ ID NO: 1, 3 or 5, or the nucleic acid sequence encoding a functional equivalent thereof, for example a sequence as shown in SEQ ID NO: 34, 36, 38, 40, 42, 44, 46, 48, 49, 51, 53, 55, 57, 61, 63, 65, 67 or 69, following Watson and Crick's base pairing rules. The antisense nucleic acid sequence can be complementary to all of the transcribed mRNA of said protein, be limited to the coding region, or else only be composed of a nucleotide, which is partially complementary to the coding or noncoding sequence of the mRNA. Thus, for example, the oligonucleotide can be complementary to the region comprising the translation start for said protein. Antisense nucleic acid sequences can be, for example, 5, 10, 15, 20, 25, 30, 35, 40, 45 or 50 nucleotides in length, but may also be longer and comprise at least 100, 200, 500, 1000, 2000 or 5000 nucleotides. Antisense nucleic acid sequences can be expressed recombinantly or synthesized chemically or enzymatically using methods known to the skilled worker. In the case of chemical synthesis, natural or modified nucleotides may be used. Modified nucleotides can impart an increased biochemical stability to the antisense nucleic acid sequence and lead to an increased physical stability of the duplex formed of antisense nucleic acid sequence and sense target sequence. The following can be used: for example phosphorothioate derivatives and acridine-substituted nucleotides such as 5-fluorouracil., 5-bromouracil, 5-chlorouracil, 5-iodouracil, hypoxanthin, xanthin, 4-acetylcytosine, 5-(carboxyhydroxylmethyl)uracil, 5-carboxymethylaminomethyl-2-thiouridine, 5-carboxymethylaminomethyluracil, dihydrouracil, β-D-galactosylqueosine, inosine, N6-isopentenyladenine, 1-methylguanine, 1-methylinosine, 2,2-dimethylguanine, 2-methyladenine, 2-methylguanine, 3-methylcytosine, 5-methylcytosine, N6-adenine, 7-methylguanine, 5-methylaminomethyluracil, 5-methoxyaminomethyl-2-thiouracil, β-D-mannosylqueosine, 5′-methoxycarboxymethyluracil, 5-methoxyuracil, 2-methylthio-N-6-isopentenyladenine, uracil-5-oxyacetic acid, pseudouracil, queosine, 2-thiocytosine, 5-methyl-2-thiouracil, 2-thiouracil, 4-thiouracil, 5-methyluracil, uracil-5-oxyacetic acid methyl ester, uracil-5-oxyacetic acid, 5-methyl-2-thiouracil, 3-(3-amino-3-N-2-carboxypropyl)uracil and 2,6-diaminopurine.

In a further preferred embodiment, the expression of an RacB protein can be inhibited by nucleotide sequences which are complementary to the regulatory region of an RacB gene (for example an RacB promoter and/or enhancer) and which form triple-helical structures with that DNA double helix so that the transcription of the RacB gene is reduced. Such methods have been described (Helene C (1991) Anticancer Drug Res 6(6):569-84; Helene C et al. (1992) Ann NY Acad Sci 660:27-36; Maher L J (1992) Bioassays 14(12):807-815). In a further embodiment, the antisense nucleic acid molecule can be an α-anomeric nucleic acid. Such α-anomeric nucleic acid molecules form specific double-stranded hybrids with complementary RNA in which—as opposed to the conventional β-nucleic acids—the two strands run parallel to one another (Gautier C et al. (1987) Nucleic Acids Res 15:6625-6641). The antisense nucleic acid molecule can furthermore also comprise 2′-O-methylribonucleotides (Inoue et al. (1987) Nucleic Acids Res 15:6131-6148) or chimeric RNA/DNA analogs (Inoue et al. (1987) FEBS Lett 215:327-330).

c) Introduction of an RacB Antisense Nucleic Acid Sequence in Combination with a Ribozyme

The above-described antisense strategy can be combined advantageously with a ribozyme method. Catalytic RNA molecules or ribozymes can be adapted to suit any target RNA and cleave the phosphodiester backbone at specific positions, functionally deactivating the target RNA (Tanner N K (1999) FEMS Microbiol Rev 23(3):257-275). The ribozyme itself is not modified thereby, but is capable of cleaving further target RNA molecules analogously, thereby assuming the qualities of an enzyme. The incorporation of ribozyme sequences into antisense RNAs confers this enzyme-like RNA-cleaving quality to precisely these antisense RNAs, thus increasing their efficacy in inactivating the target RNA. The generation and the use of such ribozyme antisense RNA molecules is described, for example, in Haseloff et al. (1988) Nature 334: 585-591.

In this manner, ribozymes (for example “hammerhead” ribozymes; Haselhoff and Gerlach (1988) Nature 334:585-591) can be used catalytically to cleave the mRNA of an enzyme to be suppressed, for example RacB, and to prevent translation. The ribozyme technique can increase the efficacy of an antisense strategy. Methods of expressing ribozymes for reducing specific proteins are described in (EP 0 291 533, EP 0 321 201, EP 0 360 257). The expression of ribozyme in plant cells has also been described (Steinecke P et al. (1992) EMBO J. 11(4):1525-1530; de Feyter R et al. (1996) Mol Gen Genet. 250(3):329-338). Suitable target sequences and ribozymes can be determined as described for example by “Steinecke P, Ribozymes, Methods in Cell Biology 50, Galbraith et al. eds, Academic Press, Inc. (1995), pp. 449-460” by calculating the secondary structure of ribozyme RNA and target RNA as well as by their interaction (Bayley CC et al. (1992) Plant Mol. Biol. 18(2):353-361; Lloyd A M and Davis R W et al. (1994) Mol Gen Genet. 242(6):653-657). For example, derivatives of the Tetrahymena L-19 IVS RNA with regions which are complementary to the mRNA of the RacB protein to be suppressed can be constructed (see also U.S. Pat. No. 4,987,071 and U.S. Pat. No. 5,116,742). As an alternative, such ribozymes can also be identified from a library of diverse ribozymes via a selection process (Bartel D and Szostak J W (1993) Science 261:1411-1418).

d) Introduction of an RacB Sense Nucleic Acid Sequence for Inducing Cosuppression

The expression of an RacB nucleic acid sequence in sense orientation can lead to cosuppression of the corresponding homologous endogenous gene. The expression of sense RNA with homology with an endogenous gene can reduce or switch off the expression of the former, similarly to what has been described for antisense approaches (Jorgensen et al. (1996) Plant Mol Biol 31(5):957-973; Goring et al. (1991) Proc Natl Acad Sci USA 88:1770-1774; Smith et al. (1990) Mol Gen Genet 224:447-481; Napoli et al. (1990) Plant Cell 2:279-289; Van der Krol et al. (1990) Plant Cell 2:291-99). In this context, the homologous gene to be reduced can be represented either fully or only in part by the construct introduced. The possibility of translation is not required. The application of this technique to plants is described, for example, by Napoli et al. (1990) The Plant Cell 2: 279-289 and in U.S. Pat. No. 5,034,323.

The cosuppression is preferably realized by using a sequence essentially identical to at least part of the nucleic acid sequence encoding an RacB protein or a functional equivalent thereof, for example the nucleic acid sequence as shown in SEQ ID NO: 1, 3 or 5, or the nucleic acid sequence encoding a functional equivalent thereof, for example a sequence as shown in SEQ ID NO: 34, 36, 38, 40, 42, 44, 46, 48, 49, 51, 53, 55, 57, 61, 63, 65, 67 or 69.

e) Introduction of Nucleic Acid Sequences Encoding a Dominant-Negative RacB Protein

The function or activity of an RacB protein can also be brought about efficiently by expressing a dominant-negative variant of this RacB protein. Methods of reducing the function or activity of a protein by coexpressing its dominant-negative form are known to the skilled worker (Lagna G and Hemmati-Brivanlou A (1998) Current Topics in Developmental Biology 36:75-98; Perlmutter R M and Alberola-Ila J (1996) Current Opinion in Immunology 8(2):285-90; Sheppard D (1994) American Journal of Respiratory Cell & Molecular Biology. 11(1):1-6; Herskowitz I (1987) Nature 329(6136):219-22).

For example, a dominant-negative RacB variant can be brought about by modifying the amino acid threonine at position 20 in the RacB proteins from maize, rice or barley to, preferably, aspartic acid. The threonine which is preferably to be mutated, or, if appropriate, also serine (similarly to threonine at position 20 in RacB from maize, rice or barley) in RacB homologs from other species can be determined for example by computer-aided comparison (“alignment”). These mutations for achieving a dominant-negative RacB variant are preferably carried out at the level of the nucleic acid sequence encoding RacB proteins. A corresponding mutation can be brought about for example by PCR-mediated in-vitro mutagenesis using suitable oligonucleotide primers, by which the desired mutation is introduced. This is done using methods known to the skilled worker; for example, the “LA PCR in vitro Mutagenesis Kit” (Takara Shuzo, Kyoto) may be used for this purpose. A method of generating a dominant-negative variant of the maize RacB protein is also described in WO 00/15815 (Example 4, p. 69).

Especially preferred are the dominant-negative variants of the RacB proteins from barley, rice or maize described under SEQ ID NO: 7, 8 and 9.

f) Introduction of DNA—or Protein-Binding Factors Against RacB Genes, RacB RNAs or RacB Proteins

RacB gene expression may also be reduced using specific DNA-binding factors, for example factors of the zinc finger transcription factor type. These factors attach to the genomic sequence of the endogenous target gene, preferably in the regulatory regions, and bring about repression of the endogenous gene. The use of such a method makes possible the reduction of the expression of an endogenous RacB gene without it being necessary to recombinantly manipulate its sequence. Suitable methods for the preparation of suitable factors have been described (Dreier B et al. (2001) J Biol Chem 276(31):29466-78; Dreier B et al. (2000) J Mol Biol 303(4):489-502; Beerli RR et al. (2000) Proc Natl Acad Sci USA 97 (4):1495-1500; Beerli R R et al. (2000) J Biol Chem 275(42):32617-32627; Segal D J and Barbas C F 3rd. (2000) Curr Opin Chem Biol 4(1):34-39; Kang J S and Kim J S (2000) J Biol Chem 275(12):8742-8748; Beerli RR et al. (1998) Proc Natl Acad Sci USA 95(25):14628-14633; Kim JS et al. (1997) Proc Natl Acad Sci USA 94(8):3616-3620; Klug A (1999) J Mol Biol 293(2):215-218; Tsai S Y et al. (1998) Adv Drug Deliv Rev 30(1-3):23-31; Mapp A K et al. (2000) Proc Natl Acad Sci USA 97(8):3930-3935; Sharrocks A D et al. (1997) Int J Biochem Cell Biol 29(12):1371-1387; Zhang L et al. (2000) J Biol Chem 275(43):33850-33860).

These factors can be selected using any desired portion of an RacB gene. This segment is preferably located in the promoter region. For gene suppression, however, it may also be in the region of the coding exons or introns. The segments in question can be obtained by the skilled worker from Genbank by database search or, starting from an RacB cDNA whose gene is not present in Genbank, by screening a genomic library for corresponding genomic clones. The skilled worker is familiar with the methods required therefor.

Furthermore, it is possible to introduce, into cells, factors which inhibit the RacB target protein itself. The protein-binding factors can be, for example, aptamers (Famulok M and Mayer G (1999) Curr Top Microbiol Immunol 243:123-36) or antibodies or antibody fragments or single-chain antibodies. Methods for obtaining these factors have been described and are known to the skilled worker. For example, a cytoplasmic scFv antibody was employed to modulate the activity of the phytochrome A protein in genetically modified tobacco plants (Owen M et al. (1992) Biotechnology (N Y) 10(7):790-794; Franken E et al. (1997) Curr Opin Biotechnol 8(4):411-416; Whitelam (1996) Trend Plant Sci 1:286-272).

Gene expression may also be suppressed by tailor-made low-molecular-weight synthetic compounds, for example of the polyamide type (Dervan P B and Bürli R W (1999) Current Opinion in Chemical Biology 3:688-693; Gottesfeld J M et al. (2000) Gene Expr 9(1-2):77-91). These oligomers are composed of the units 3-(dimethylamino)propylamine, N-methyl-3-hydroxypyrrole, N-methylimidazole and N-methylpyrrole and can be adapted to any piece of double-stranded DNA in such a way that they bind into the major groove in a sequence-specific manner and block the expression of these gene sequences. Suitable methods have been described (see, inter alia, Bremer R E et al. (2001) Bioorg Med Chem. 9(8):2093-103; Ansari A Z et al. (2001) Chem Biol. 8(6):583-92; Gottesfeld J M et al. (2001) J. Mol. Biol. 309(3):615-29; Wurtz N R et al. (2001) Org Lett 3(8):1201-3; Wang CC et al. (2001) Bioorg Med Chem 9(3):653-7; Urbach A R and Dervan PB (2001) Proc Natl Acad Sci USA 98(8):4343-8; Chiang S Y et al. (2000) J. Biol. Chem. 275(32):24246-54).

g) Introduction of Viral Nucleic Acid Sequences and Expression Constructs which Cause RacB RNA Degradation

RacB expression can also be brought about efficiently by inducing the specific RacB RNA degradation by the plant with the aid of a viral expression system (amplicon) (Angell, S M et al. (1999) Plant J. 20(3):357-362). These systems—also termed “VIGS” (viral induced gene silencing)—introduce, into the plant, nucleic acid sequences with homology to the transcripts to be suppressed, with the aid of viral vectors. Then, transcription is switched off, probably mediated by plant defense mechanisms against viruses. Suitable techniques and methods have been described (Ratcliff F et al. (2001) Plant J 25(2):237-45; Fagard M and Vaucheret H (2000) Plant Mol Biol 43(2-3):285-93; Anandalakshmi R et al. (1998) Proc Natl Acad Sci USA 95(22):13079-84; Ruiz M T (1998) Plant Cell 10(6): 937-46).

h) Introduction of Constructs for Inducing a Homologous Recombination on Endogenous RacB Genes, for Example for Generating Knock-Out Mutants

An example of what is used for generating a homologously recombinant organism with reduced RacB activity is a nucleic acid construct comprising at least part of an endogenous RacB gene which is modified by a deletion, addition or substitution of at least one nucleotide in such a way that its functionality is reduced or fully destroyed. The modification may also relate to the regulatory elements (for example the promoter) of the gene, so that the coding sequence remains unmodified, but expression (transcription and/or translation) does not take place and is reduced.

In the case of conventional homologous recombination, the modified region is flanked at its 5′ and 3′ end by further nucleic acid sequences which must be sufficient in length for making possible recombination. They are, as a rule, in the range of several hundred bases to several kilobases in length (Thomas K R and Capecchi M R (1987). Cell 51:503; Strepp et al. (1998) Proc Natl Acad Sci USA 95(8):4368-4373). For homologous recombination, the host organism—for example a plant—is transformed with the recombination construct using the methods described hereinbelow, and clones which have successfully undergone recombination are selected, for example using a resistance to antibiotics or herbicides.

Homologous recombination is a relatively rare event in higher eukaryotes, especially in plants. Random integrations into the host genome predominate. One possibility of eliminating the randomly integrated sequences and thus increasing the number of cell clones with a correct homologous recombination is the use of a sequence-specific recombination system as described in U.S. Pat. No. 6,110,736, by which unspecifically integrated sequences can be deleted again, which simplifies the selection of events which have integrated successfully via homologous recombination. A large number of sequence-specific recombination systems can be used, examples being the Cre/lox system of bacteriophage P1, the FLP/FRT system of yeast, the Gin recombinase of phage Mu, the Pin recombinase from E. coli, and the R/RS system of the pSR1 plasmid. The bacteriophage P1 Cre/10× and the yeast FLP/FRT system are preferred. The FLP/FRT and cre/lox recombinase system has already been applied to plant systems (Odell et al. (1990) Mol Gen Genet 223: 369-378).

i) Introduction of Mutations into Endogenous RacB Genes for Generating a Loss of Function (For Example Generation of Stop Codons, Reading-Frame Shifts and the Like)

Further suitable methods for reducing the RacB activity are the introduction of nonsense mutations into endogenous RacB genes, for example by introducing RNA/DNA oligonucleotides into the plant (Zhu et al. (2000) Nat Biotechnol 18(5):555-558) and the generation of knock-out mutants with the aid of, for example, T-DNA mutagenesis (Koncz et al. (1992) Plant Mol Biol 20(5):963-976), ENU (N-ethyl-N-nitrosourea) mutagenesis or homologous recombination (Hohn B and Puchta (1999) H Proc Natl Acad Sci USA 96:8321-8323.). Point mutations can also be generated by means of DNA-RNA hybrids also known under the name “chimeraplasty” (Cole-Strauss-et al. (1999) Nucl Acids Res. 27(5):1323-1330; Kmiec (1999) Gene therapy American Scientist 87(3):240-247).

The methods of dsRNAi, cosuppression by means of sense RNA and “VIGS” (“virus induced gene silencing”) are also termed “post-transcriptional gene silencing” (PTGS). PTGS methods, like the reduction of the RacB function or activity with dominant-negative RacB variants, are especially advantageous because the demands regarding the homology between the endogenous gene to be suppressed and the sense or dsRNA nucleic acid sequence expressed recombinantly (or between the endogenous gene and its dominant-negative variant) are lower than, for example, in the case of a traditional antisense approach. Such criteria with regard to homology are mentioned in the description of the dsRNAI method and can generally be applied to PTGS methods or dominant-negative approaches. Owing to the high degree of homology between the RacB proteins from maize, rice and barley, a high degree of conservation of this protein in plants can be assumed. Thus, using the RacB nucleic acid sequences from barley, maize or rice, it is presumably also possible efficiently to suppress the expression of homologous RacB proteins in other species without the isolation and structure elucidation of the RacB homologs occurring therein being required. Considerably less labor is therefore required. Similarly, the use of dominant-negative variants of an RacB protein from rice, maize or barley can presumably also efficiently reduce or suppress the function/activity of its homolog in other plant species.

All of the substances and compounds which directly or indirectly bring about a reduction in protein quantity, RNA quantity, gene activity or protein activity of an RacB protein shall subsequently be combined in the term “anti-RacB” compounds. The term “anti-RacB” compound explicitly includes the nucleic acid sequences, peptides, proteins or other factors employed in the above-described methods.

For the purposes of the invention, “introduction” comprises all of the methods which are capable of directly or indirectly introducing an “anti-RacB” compound into a plant or a cell, compartment, tissue, organ or seed thereof, or of generating such a compound there. Direct and indirect methods are comprised. The introduction can lead to a transient presence of an “anti-RacB” compound (for example a dsRNA) or else to its stable presence.

Owing to the different nature of the above-described approaches, the “anti-RacB” compound can exert its function directly (for example by insertion into an endogenous RacB gene). However, its function can also be exerted indirectly following transcription into an RNA (for example in the case of antisense approaches) or following transcription and translation into a protein (for example in the case of binding factors). The invention comprises both directly and indirectly acting “anti-RacB” compounds.

The term “introducing” comprises for example methods such as transfection, transduction or transformation.

“Anti-RacB” compounds therefore also comprises recombinant expression constructs which bring about expression (i.e. transcription and, if appropriate, translation), for example of an RacB dsRNA or an RacB “antisense” RNA, preferably in a plant or a part, tissue, organ or seed thereof.

In said expression constructs, a nucleic acid molecule whose expression (transcription and, if appropriate, translation) generates an “anti-RacB” compound is preferably operably linked to at least one genetic control element (for example a promoter) which ensures expression in an organism, preferably in plants. If the expression construct is to be introduced directly into a plant and the “anti-RacB” compound (for example the RacB dsRNA) is to be generated therein in plantae, plant-specific genetic control elements (for example promoters) are preferred. However, the “anti-RacB” compound may also be generated in other organisms or in vitro and then be introduced into the plant (as described in Examples 6 and 7). Preferred in this context are all of the prokaryotic or eukaryotic genetic control elements (for example promoters) which permit the expression in the organism chosen in each case for the preparation.

Operable linkage is to be understood as meaning, for example, the sequential arrangement of a promoter with the nucleic acid sequence to be expressed (for example an “anti-RacB” compound) and, if appropriate, further regulatory elements such as, for example, a terminator in such a way that each of the regulatory elements can fulfil its function when the nucleic acid sequence is expressed recombinantly, depending on the arrangement of the nucleic acid sequences in relation to sense or antisense RNA. To this end, direct linkage in the chemical sense is not necessarily required. Genetic control sequences such as, for example, enhancer sequences, can also exert their function on the target sequence from positions which are further away, or indeed from other DNA molecules. Preferred arrangements are those in which the nucleic acid sequence to be expressed recombinantly is positioned behind the sequence acting as promoter, so that the two sequences are linked covalently to each other. The distance between the promoter sequence and the nucleic acid sequence to be expressed recombinantly is preferably less than 200 base pairs, especially preferably less than 100 base pairs, very especially preferably less than 50 base pairs.

Operable linkage, and an expression cassette, can be generated by means of customary recombination and cloning techniques as are described, for example, in Maniatis T, Fritsch E F and Sambrook J (1989) Molecular Cloning: A Laboratory Manual, Cold Spring Harbor Laboratory, Cold Spring Harbor (NY), in Silhavy T J, Berman M L and Enquist L W (1984) Experiments with Gene Fusions, Cold Spring Harbor Laboratory, Cold Spring Harbor (NY), in Ausubel FM et al. (1987) Current Protocols in Molecular Biology, Greene Publishing Assoc. and Wiley Interscience and in Gelvin et al. (1990) In: Plant Molecular Biology Manual. However, further sequences which, for example, act as a linker with specific cleavage sites for restriction enzymes, or as a signal peptide, may also be positioned between the two sequences. The insertion of sequences may also lead to the expression of fusion proteins. Preferably, the expression cassette, consisting of a linkage of promoter and nucleic acid sequence to be expressed, can exist in a vector-integrated form and be inserted into a plant genome, for example by transformation.

However, expression cassette also denotes those constructions in which a promoter is positioned behind an endogenous RacB gene, for example by means of homologous recombination, and the reduction according to the invention of an RacB protein is brought about by the expression of an antisense RacB RNA.

Analogously, an “anti-RacB” compound (for example a nucleic acid sequence encoding an RacB dsRNA or an RacB antisense RNA) can be positioned behind an endogenous promoter in such a way that the same effect is manifested. Both approaches lead to inventive expression cassettes.

The term plant-specific promoters is understood as meaning, in principle, any promoter which is capable of governing the expression of genes, in particular foreign genes, in plants or plant parts, plant cells, plant tissues or plant cultures. In this context, expression can be, for example, constitutive, inducible or development-dependent.

The following are preferred:

a) Constitutive Promoters

Preferred vectors are those which make possible constitutive expression in plants (Benfey et al. (1989) EMBO J. 8:2195-2202). “Constitutive” promoter is understood as meaning those promoters which ensure expression in a large number of, preferably all, tissues over a substantial period of plant development, preferably at all stages of plant development. In particular a plant promoter or a promoter derived from a plant virus are preferably used. Particularly preferred is the promoter of the CaMV cauliflower mosaic virus ³⁵S transcript (Franck et al. (1980) Cell 21:285-294; Odell et al. (1985) Nature 313:810-812; Shewmaker et al. (1985) Virology 140:281-288; Gardner et al. (1986) Plant Mol Biol 6:221-228) or the 19S CaMV promoter (U.S. Pat. No. 5,352,605; WO 84/02913; Benfey et al. (1989) EMBO J. 8:2195-2202). Another suitable constitutive promoter is the “Rubisco small subunit (SSU)” promoter (U.S. Pat. No. 4,962,028), the leguminB promoter (GenBank Acc. No. X03677), the Agrobacterium nopaline synthase promoter, the TR dual promoter, the Agrobacterium OCS (octopine synthase) promoter, the ubiquitin promoter (Holtorf S et al. (1995) Plant Mol Biol 29:637-649), the ubiquitin 1 promoter (Christensen et al. (1992) Plant Mol Biol 18:675-689; Bruce et al. (1989) Proc Natl Acad Sci USA 86:9692-9696), the Smas promoter, the cinnamyl alcohol dehydrogenase promoter (U.S. Pat. No. 5,683,439), the promoters of the vacuolar ATPase subunits or the promoter of a proline-rich protein from wheat (WO 91/13991), and further promoters of genes whose constitutive expression in plants is known to the skilled worker. A particularly preferred constitutive promoter is the promoter of the nitrilase-1 (nit1) gene from A. thaliana (GenBank Acc.-No.: Y07648.2, nucleotides 2456-4340, Hillebrand et al. (1996) Gene 170:197-200).

b) Tissue-Specific Promoters

Preferred are furthermore promoters with specificity for the anthers, ovaries, flowers, leaves, stems, roots and seeds.

Seed-Specific Promoters

such as, for example, the phaseolin promoter (U.S. Pat. No. 5,504,200; Bustos M M et al. (1989) Plant Cell 1(9):839-53), the 2S albumin gene promoter (Joseffson L G et al. (1987) J Biol Chem 262:12196-12201), the legumin promoter (Shirsat A et al. (1989) Mol Gen Genet 215(2): 326-331), the USP (unknown seed protein) promoter (Baumlein H et al. (1991) Mol Gen Genet 225(3):459-67), the napin gene promoter (U.S. Pat. No. 5,608,152; Stalberg K et al. (1996) L Planta 199:515-519), the sucrose binding protein promoter (WO 00/26388) or the legumin B4 promoter (LeB4; Bäumlein H et al. (1991) Mol Gen Genet 225: 121-128; Baeumlein et al. (1992) Plant Journal 2(2):233-9; Fiedler U et al. (1995) Biotechnology (NY) 13(10):1090f), the Arabidopsis oleosin promoter (WO 98/45461), the Brassica Bce4 promoter (WO 91/13980). Further suitable seed-specific promoters are those of the genes encoding the high-molecular-weight glutenin (HMWG), gliadin, branching enzyme, ADP glucose pyrophosphatase (AGPase) or starch synthase. Furthermore preferred are promoters which permit seed-specific expression in monocots such as maize, barley, wheat, rye, rice and the like. The following can be employed advantageously: the promoter of the lpt2 or lpt1 gene (WO 95/15389, WO 95/23230) or the promoters described in WO 99/16890 (promoters of the hordein gene, the glutelin gene, the oryzin gene, the prolamin gene, the gliadin gene, the glutelin gene, the zein gene, the kasirin gene or the secalin gene).

Tuber-, storage-root- or root-specific promoters such as, for example, the patatin promoter class I (B33), the potato cathepsin D inhibitor promoter.

Leaf-Specific Promoters

such as the potato cytosolic FBPase promoter (WO 97/05900), the Rubisco (ribulose-1,5-bisphosphate carboxylase) SSU (small subunit) promoter or the ST-LSI promoter from potato (Stockhaus et al. (1989) EMBO J. 8:2445-2451). Very especially preferred are epidermis-specific promoters such as, for example, the OXLP gene (oxalate-oxidase-like protein) promoter (Wei et al. (1998) Plant Mol. Biol. 36:101-112).

Flower-Specific Promoters

such as, for example, the phytoene synthase promoter (WO 92/16635) or the promoter of the P-rr gene (WO 98/22593).

Anther-Specific Promoters

such as the 5126 promoter (U.S. Pat. No. 5,689,049, U.S. Pat. No. 5,689,051), the glob-1 promoter and the γ-zein promoter.

c) Chemically Inducible Promoters

The expression cassettes can also comprise a chemically inducible promoter (review article: Gatz et al. (1997) Annu Rev Plant Physiol Plant Mol Biol 48:89-108), by which the expression of the exogenous gene in the plant at a particular point in time can be controlled. Such promoters such as, for example, the PRP1 promoter (Ward et al. (1993) Plant Mol Biol 22:361-366), a salicylic-acid-inducible promoter (WO 95/19443), a benzenesulfonamide-inducible promoter (EP 0 388.186), a tetracyclin-inducible promoter (Gatz et al. (1992) Plant J 2:397-404)., an abscisic-acid-inducible promoter (EP 0 335 528) or an ethanol- or cyclohexanone-inducible promoter (WO 93/21334) can likewise be used.

d) Stress- or Pathogen-Inducible Promoters

Further preferred promoters are those which are induced by biotic or abiotic stress such as, for example, the pathogen-inducible promoter of the PRP1 gene (or gst1 promoter) e.g. from potato (WO 96/28561; Ward et al. (1993) Plant Mol Biol 22:361-366), the tomato high-temperature-inducible hsp70 or hsp80 promoter (U.S. Pat. No. 5,187,267), the potato low-temperature-inducible alpha-amylase promoter (WO 96/12814), the light-inducible PPDK promoter, or the wounding-induced pinII promoter (EP-A 0 375 091).

Further pathogen-inducible promoters comprise the Fis1 promoter from flax (WO 96/34949), the Vst1 promoter (Schubert et al. (1997) Plant Mol Biol 34:417-426) and the EAS4 sesquiterpene cyclase promoter from tobacco (U.S. Pat. No. 6,100,451).

Pathogen-inducible promoters comprise those of genes which are induced as a consequence of infection by pathogens, such as, for example, genes of PR proteins, SAR proteins, β-1,3-glucanase, chitinase and the like (for example Redolfi et al. (1983) Neth J Plant Pathol 89:245-254; Uknes, et al. (1992) The Plant Cell 4:645-656; Van Loon (1985) Plant Mol Viral 4:111-116; Marineau et al. (1987) Plant Mol Biol 9:335-342; Matton et al. (1987) Molecular Plant-Microbe Interactions 2:325-342; Somssich et al. (1986) Proc Natl Acad Sci USA 83:2427-2430; Somssich et al. (1988) Mol Gen Genetics 2:93-98; Chen et al. (1996) Plant J 10:955-966; Zhang and Sing (1994) Proc Natl Acad Sci USA 91:2507-2511; Warner, et al. (1993) Plant J 3:191-201; Siebertz et al. (1989) Plant Cell 1:961-968(1989).

Also comprised are wounding-inducible promoters such as that of the pinII gene (Ryan (1990) Ann Rev Phytopath 28:425-449; Duan et al. (1996) Nat Biotech 14:494-498), of the wun1 and wun2 gene (U.S. Pat. No. 5,428,148), of the win1 and win2 gene (Stanford et al. (1989) Mol Gen Genet 215:200-208), of system in (McGurl et al. (1992) Science 225:1570-1573), of the WIP1 gene (Rohmeier et al. (1993) Plant Mol Biol 22:783-792; Eckelkamp et al. (1993). FEBS Letters 323:73-76), of the MPI gene (Corderok et al. (1994) Plant J 6(2):141-150) and the like.

A source of further pathogen-inducible promoters is the PR gene family. A number of elements in these promoters have been found to be advantageous. Thus, the region −364 to −288 in the promoter of PR-2d provides salicylate specificity (Buchel et al. (1996) Plant Mol Biol 30, 493-504). The sequence 5′-TCATCTTCTT-3′ is encountered repeatedly in the promoter of barley β-1,3-glucanase and more than 30 further stress-induced genes. In tobacco, this region binds a nuclear protein whose abundance is increased by salicylate. The PR-1 promoters from tobacco and Arabidopsis (EP-A 0 332 104, WO 98/03536) are likewise suitable for use as pathogen-inducible promoters. “Acidic PR-5′-(aPR5)-promoters from barley (Schweizer et al. (1997) Plant Physiol 114:79-88) and wheat (Rebmann et al. (1991) Plant Mol Biol 16:329-331) are preferred, since they are particularly specifically pathogen-induced. aPR5 proteins accumulate within about 4 to 6 hours after pathogen attack and have only very limited background expression (WO 99/66057). One approach to achieve higher pathogen-induced specificity is the preparation of synthetic promoters from combinations of known pathogen-responsive elements (Rushton et al. (2002) Plant Cell 14, 749-762; WO 00/01830; WO 99/66057). Further pathogen-inducible promoters from different species are known to the person skilled in the art (EP-A 1 165 794; EP-A 1 062 356; EP-A 1 041 148; EP-A 1 032 684;

e) Development-Dependent Promoters

Further suitable promoters are, for example, fruit-maturation-specific promoters such as, for example, the tomato fruit-maturation-specific promoter (WO 94/21794, EP 409 625). Development-dependent promoters comprise partly the tissue-specific promoters, since individual tissues develop by nature in a development-dependent fashion.

Especially preferred are constitutive promoters and leaf- and/or stem-specific, pathogen-inducible and epidermis-specific promoters, with pathogen-inducible and epidermis-specific promoters being most preferred.

Furthermore, further promoters may be linked operably to the nucleic acid sequence to be expressed, which promoters make possible the expression in further plant tissues or in other organisms, such as, for example, E. coli bacteria. Suitable plant promoters are, in principle, all of the above-described promoters.

The nucleic acid sequences present in the expression cassettes or vectors according to the invention can be linked operably to further genetic control sequences in addition to a promoter. The term “genetic control sequences” is to be understood in the broad sense and refers to all those sequences which have an effect on the materialization or the function of the expression cassette according to the invention. For example, genetic control sequences modify the transcription and translation in prokaryotic or eukaryotic organisms. Preferably, the expression cassettes according to the invention comprise the promoter with specificity for the embryonal epidermis and/or the flower 5′-upstream of the nucleic acid sequence in question to be expressed recombinantly, and 3′-downstream a terminator sequence as additional genetic control sequence and, if appropriate, further customary regulatory elements, in each case linked operably to the nucleic acid sequence to be expressed recombinantly.

Genetic control sequences also comprise further promoters, promoter elements or minimal promoters, all of which can modify the expression-governing properties. Thus, for example, the tissue-specific expression may additionally depend on certain stressors, owing to genetic control sequences. Such elements have been described, for example, for water stress, abscisic acid (Lam E and Chua N H, J Biol Chem 1991; 266(26): 17131-17135) and heat stress (Schoffl F et al., Molecular & General Genetics 217(2-3):246-53, 1989).

Further advantageous control sequences are, for example, in the Gram-positive promoters amy and SPO2, and in the yeast or fungal promoters ADC1, MFa, AC, P-60, CYC1, GAPDH, TEF, rp28, ADH.

In principle, all natural promoters with their regulatory sequences like those mentioned above may be used for the method according to the invention. In addition, synthetic promoters may also be used advantageously.

Genetic control sequences furthermore also comprise the 5′-untranslated regions, introns or noncoding 3′-region of genes, such as, for example, the actin-1 intron, or the Adh1-S introns 1, 2 and 6 (general reference: The Maize Handbook, Chapter 116, Freeling and Walbot, Eds., Springer, New York (1994)). It has been demonstrated that they may play a significant roles in the regulation of gene expression. Thus, it has been demonstrated that 5′-untranslated sequences can enhance the transient expression of heterologous genes. Examples of translation enhancers which may be mentioned are the tobacco mosaic virus 5′ leader sequence (Gallie et al. (1987) Nucl Acids Res 15:8693-8711) and the like. Furthermore, they may promote tissue specificity (Rouster J et al. (1998) Plant J 15:435-440).

The expression cassette may advantageously comprise one or more of what are known as enhancer sequences, linked operably to the promoter, which make possible an increased recombinant expression of the nucleic acid sequence. Additional advantageous sequences, such as further regulatory elements or terminators, may also be inserted at the 3′ end of the nucleic acid sequences to be expressed recombinantly. One or more copies of the nucleic acid sequences to be expressed recombinantly may be present in the gene construct.

Polyadenylation signals which are suitable as control sequences are plant polyadenylation signals, preferably those which essentially correspond to T-DNA polyadenylation signals from Agrobacterium tumefaciens, in particular gene 3 of the T-DNA (octopin synthase) of the Ti plasmid pTiACHS (Gielen et al. (1984) EMBO J. 3:835 et seq.) or functional equivalents thereof. Examples of terminator sequences which are especially suitable are the OCS (octopin synthase) terminator and the NOS (nopalin synthase) terminator.

Control sequences are furthermore to be understood as those which make possible homologous recombination or insertion into the genome of a host organism or which permit removal from the genome. In the case of homologous recombination, for example the natural promoter of a particular gene may be exchanged for a promoter with specificity for the embryonal epidermis and/or the flower. Methods such as the cre/lox technology permit a tissue-specific, if appropriate inducible, removal of the expression cassette from the genome of the host organism (Sauer B (1998) Methods. 14(4):381-92). In this method, specific flanking sequences (lox sequences), which later allow removal by means of cre recombinase, are attached to the target gene.

An expression cassettes and the vectors derived from it may comprise further functional elements. The term functional element is to be understood in the broad sense and refers to all those elements which have an effect on the generation, amplification or function of the expression cassettes, vectors or transgenic organisms according to the invention. The following may be mentioned by way of example, but not by limitation:

-   -   a) Selection markers which confer a resistance to a metabolism         inhibitor such as 2-deoxyglucose-6-phosphate (WO 98/45456),         antibiotics or biocides, preferably herbicides, such as, for         example, kanamycin, G 418, bleomycin or hygromycin, or else         phosphinothricin and the like. Especially preferred selection         markers are those which confer resistance to herbicides.         Examples which may be mentioned are: DNA sequences which encode         phosphinothricin acetyl transferases (PAT) and which inactivate         glutamin synthase inhibitors (bar and pat genes),         5-enolpyruvylshikimate-3-phosphate synthase genes (EPSP synthase         genes), which confer resistance to Glyphosate®         (N-(phosphonomethyl)glycine), the gox gene, which encodes         Glyphosate®-degrading enzymes (Glyphosate oxidoreductase), the         deh gene (encoding a dehalogenase which inactivates dalapon),         sulfonylurea- and imidazolinone-inactivating acetolactate         synthases, and bxn genes, which encode bromoxynil-degrading         nitrilase enzymes, the aasa gene, which confers resistance to         the antibiotic apectinomycin, the streptomycin         phosphotransferase (SPT) gene, which allows resistance to         streptomycin, the neomycin phosphotransferase (NPTII) gene,         which confers resistance to kanamycin or geneticidin, the         hygromycin phosphotransferase (HPT) gene, which mediates         resistance to hygromycin, the acetolactate synthase gene (ALS),         which confers resistance to sulfonylurea herbicides (for example         mutated ALS variants with, for example, the S4 and/or Hra         mutation).     -   b) Reporter genes which encode readily quantifiable proteins         and, via their color or enzyme activity, make possible an         assessment of the transformation efficacy, the site of         expression or the time of expression. Very especially preferred         in this context are genes encoding reporter proteins (Schenborn         E, Groskreutz D. Mol Biotechnol. 1999; 13(1):29-44) such as the         green fluorescent protein (GFP). (Sheen et al. (1995) Plant         Journal 8(5):777-784; Haseloff et al. (1997) Proc Natl Acad Sci         USA 94(6):2122-2127; Reichel et al. (1996) Proc Natl Acad Sci         USA 93(12):5888-5893; Tian et al. (1997) Plant Cell Rep         16:267-271; WO 97/41228; Chui WL et al. (1996) Curr Biol         6:325-330; Leffel SM et al. (1997) Biotechniques. 23(5):912-8),         chloramphenicol transferase, a luciferase (Ow et al. (1986)         Science 234:856-859; Millar et al. (1992) Plant Mol Biol Rep         10:324-414), the aequorin gene (Prasher et al. (1985) Biochem         Biophys Res Commun 126(3):1259-1268), β-galactosidase, R locus         gene (encoding a protein which regulates the production of         anthocyanin pigments (red coloring) in plant tissue and thus         makes possible the direct analysis of the promoter activity         without addition of further auxiliary substances or chromogenic         substrates; Dellaporta et al., In: Chromosome Structure and         Function: Impact of New Concepts, 18th Stadler Genetics         Symposium, 11:263-282, 1988), with β-glucuronidase being very         especially preferred (Jefferson et al., EMBO J. 1987, 6,         3901-3907).     -   c) Origins of replication, which ensure amplification of the         expression cassettes or vectors according to the invention in,         for example, E. coli. Examples which may be mentioned are ORI         (origin of DNA replication), the pBR322 ori or the P15A ori         (Sambrook et al.: Molecular Cloning. A Laboratory Manual, 2nd         ed. Cold Spring Harbor Laboratory Press, Cold Spring Harbor,         N.Y., 1989).     -   d) Elements which are necessary for Agrobacterium-mediated plant         transformation, such as, for example, the right or left border         of the T-DNA or the vir region.

To select cells which have successfully undergone homologous recombination, or else to select transformed cells, it is, as a rule, necessary additionally to introduce a selectable marker, which confers resistance to a biocide (for example herbicide), a metabolism inhibitor such as 2-deoxyglucose-6-phosphate (WO 98/45456) or an antibiotic to the cells which have successfully undergone recombination. The selection marker permits the selection of the transformed cells from untransformed ones (McCormick et al. (1986) Plant Cell Reports 5:81-84).

The introduction of an expression cassette according to the invention into an organism or cells, tissues, organs, parts or seeds thereof (preferably into plants or plant cells, tissue, organs, parts or seeds) can be effected advantageously using vectors which comprise the expression cassettes. The expression cassette can be introduced into the vector (for example a plasmid) via a suitable restriction cleavage site. The plasmid formed is first introduced into E. coli. Correctly transformed E. coli are selected, grown, and the recombinant plasmid is obtained by the methods familiar to the skilled worker. Restriction analysis and sequencing may serve to verify the cloning step.

Examples of vectors may be plasmids, cosmids, phages, viruses or else agrobacteria. In an advantageous embodiment, the expression cassette is introduced by means of plasmid vectors. Preferred vectors are those which make possible stable integration of the expression cassette into the host genome.

The generation of a transformed organism (or of a transformed cell or tissue) requires introducing the DNA, RNA or protein in question into the relevant host cell.

A multiplicity of methods are available for this procedure, which is termed transformation (or transduction or transfection) (Keown et al. (1990) Methods in Enzymology 185:527-537). For example, the DNA or RNA can be introduced directly by microinjection or by bombardment with DNA-coated microparticles. Also, the cell can be permeabilized chemically, for example using polyethylene glycol, so that DNA can enter the cell by diffusion. The DNA can also be introduced by protoplast fusion with other DNA-containing units such as minicells, cells, lysosomes or liposomes. Another suitable method of introducing DNA is electroporation, where the cells are permeabilized reversibly by an electrical pulse. Suitable methods have been described (for example by Bilang et al. (1991) Gene 100:247-250; Scheid et al. (1991) Mol Gen Genet 228:104-112; Guerche et al. (1987) Plant Science 52:111-116; Neuhause et al. (1987) Theor Appl Genet 75:30-36; Klein et al. (1987) Nature 327:70-73; Howell et al. (1980) Science 208:1265; Horsch et al. (1985) Science 227:1229-1231; DeBlock et al. (1989) Plant Physiology 91:694-701; Methods for Plant Molecular Biology (Weissbach and Weissbach, eds.) Academic Press Inc. (1988); and Methods in Plant Molecular Biology (Schuler and Zielinski, eds.) Academic Press Inc. (1989)).

In plants, the above-described methods of transforming and regenerating plants from plant tissues or plant cells are exploited for transient or stable transformation. Suitable methods are especially protoplast transformation by polyethylene-glycol-induced DNA uptake, the biolistic method with the gene gun, what is known as the particle bombardment method, electroporation, incubation of dry embryos in DNA-containing solution, and microinjection.

In addition to these “direct” transformation techniques, transformation can also be effected by bacterial infection by means of Agrobacterium tumefaciens or Agrobacterium rhizogenes. The Agrobacterium-mediated transformation is best suited to dicotyledonous plant cells. The methods are described, for example, by Horsch RB et al. (1985) Science 225: 1229f.

When agrobacteria are used, the expression cassette must be integrated into specific plasmids, either into a shuttle or intermediate vector, or into a binary vector. If a Ti or Ri plasmid is to be used for the transformation, at least the right border, but in most cases the right and left border, of the Ti or Ri plasmid T-DNA is linked to the expression cassette to be introduced in the form of a flanking region.

Binary vectors are preferably used. Binary vectors are capable of replication both in E. coli and in Agrobacterium. As a rule, they comprise a selection marker gene and a linker or polylinker flanked by the right and left T-DNA border sequence. They can be transferred directly into Agrobacterium (Holsters et al. (1978) Mol Gen Genet 163:181-187). The selection marker gene permits the selection of transformed agrobacteria and is, for example, the nptII gene, which confers resistance to kanamycin. The Agrobacterium which acts as host organism in this case should already contain a plasmid with the vir region. The latter is required for transferring the T-DNA to the plant cell. An Agrobacterium transformed in this way can be used for transforming plant cells. The use of T-DNA for transforming plant cells has been studied and described intensively (EP 120 516; Hoekema, In: The Binary Plant Vector System, Offsetdrukkerij Kanters B. V., Alblasserdam, Chapter V; An et al. (1985) EMBO J. 4:277-287). Various binary vectors are known, some of which are commercially available such as, for example, pBI101.2 or pBIN19 (Clontech Laboratories, Inc. USA).

Further promoters which are suitable for expression in plants have been described (Rogers et al. (1987) Meth in Enzymol 153:253-277; Schardl et al. (1987) Gene 61:1-11; Berger et al. (1989) Proc Natl Acad Sci USA 86:8402-8406).

Direct transformation techniques are suitable for any organism and cell type.

The plasmid used need not meet any particular requirements in the case of the injection or electroporation of DNA or RNA into plant cells. Simple plasmids such as those of the pUC series can be used. If complete plants are to be regenerated from the transformed cells, it is necessary for an additional selectable marker gene to be located on the plasmid.

Stably transformed cells, i.e. those which contain the introduced DNA integrated into the DNA of the host cell, can be selected from untransformed cells when a selectable marker is part of the DNA introduced. Examples of genes which can act as markers are all those which are capable of conferring resistance to antibiotics or herbicides (such as kanamycin, G 418, bleomycin, hygromycin or phosphinothricin) (see above). Transformed cells which express such marker genes are capable of surviving in the presence of concentrations of a corresponding antibiotic or herbicide which kill an untransformed wild type. Examples are mentioned above and preferably comprise the bar gene, which confers resistance to the herbicide phosphinothricin (Rathore K S et al. (1993) Plant Mol Biol 21(5):871-884), the nptII gene, which confers resistance to kanamycin, the hpt gene, which confers resistance to hygromycin, or the EPSP gene, which confers resistance to the herbicide Glyphosate. The selection marker permits the selection of transformed cells from untransformed cells (McCormick et al. (1986) Plant Cell Reports 5:81-84). The resulting plants can be bred and hybridized in the customary fashion. Two or more generations should be grown in order to ensure that the genomic integration is stable and hereditary.

The abovementioned methods are described, for example, in Jenes B et al. (1993) Techniques for Gene Transfer, in: Transgenic Plants, Vol. 1, Engineering and Utilization, edited by SD Kung and R Wu, Academic Press, pp. 128-143 and in Potrykus (1991) Annu Rev Plant Physiol Plant Molec Biol 42:205-225). The construct to be expressed is preferably cloned into a vector which is suitable for the transformation of Agrobacterium tumefaciens, for example pBin19 (Bevan et al. (1984) Nucl Acids Res 12:8711f).

As soon as a transformed plant cell has been generated, a complete plant can be obtained using methods known to the skilled worker. For example, callus cultures are used as starting material. The development of shoot and root can be induced in this as yet undifferentiated cell biomass in a known fashion. The shoots obtained can be planted out and bred.

The skilled worker is familiar with such methods of regenerating plant parts and intact plants from plant cells. Methods to do so are described, for example, by Fennell et al. (1992) Plant Cell Rep. 11: 567-570; Stoeger et al (1995) Plant Cell Rep. 14:273-278; Jahne et al. (1994) Theor Appl Genet 89:525-533.

The method according to the invention can advantageously be combined with further methods which bring about pathogen resistance (for example to insects, fungi, bacteria, nematodes and the like), stress resistance or another improvement of the plant properties. Examples are mentioned, inter alia, by Dunwell J M, Transgenic approaches to crop improvement, J Exp Bot. 2000;51 Spec No; pages 487-96.

The invention furthermore relates to the barley RacB protein as shown in SEQ ID NO: 2, and to dominant-negative variant thereof, for example described by SEQ ID NO: 7.

The invention furthermore relates to nucleic acid sequences encoding the barley RacB protein, preferably the nucleic acid sequence as shown in SEQ ID NO: 1, the nucleic acid sequence complementary thereto, and the sequences derived owing to degeneracy of the genetic code.

The invention furthermore relates to the polypeptide encoding functional equivalents of the RacB protein from barley as shown in SEQ ID NO: 35, 37 or 39.

The invention furthermore relates to nucleic acid sequences encoding functional equivalents of the RacB protein from barley, preferably the nucleic acid sequence as shown in SEQ ID NO: 34, 36 or 38, the nucleic acid sequence complementary thereto and the sequences derived by degeneration of the genetic code.

The invention furthermore relates to transgenic expression cassettes comprising one of the nucleic acid sequences according to the invention. In the transgenic expression cassettes according to the invention, the nucleic acid sequence encoding the barley RacB protein is linked to at least one genetic control element as defined above in such a manner that it is capable of expression (transcription and, if appropriate, translation) in any organism, preferably in plants. Suitable genetic control elements are described above. The transgenic expression cassettes may also comprise further functional elements in accordance with the above definition. The inserted nucleic acid sequence encoding a barley RacB protein can be inserted in the expression cassette in sense or antisense orientation and thus lead to the expression of sense or antisense RNA. Transgenic vectors comprising the transgenic expression cassettes are also in accordance with the invention.

“Transgenic”, for example regarding a nucleic acid sequence, an expression cassette or a vector comprising said nucleic acid sequence or an organism transformed with said nucleic acid sequence, expression cassette or vector, refers to all those constructs originating by recombinant methods in which either

-   a) the RacB nucleic acid sequence, or -   b) a genetic control sequence linked operably to the RacB nucleic     acid sequence, for example a promoter, or -   c) (a) and (b) are not located in their natural genetic environment     or have been modified by recombinant methods, an example of a     modification being a substitutions, additions, deletions, inversion     or insertions of one or more nucleotide residues. Natural genetic     environment refers to the natural chromosomal locus in the organism     of origin, or to the presence in a genomic library. In the case of a     genomic library, the natural genetic environment of the nucleic acid     sequence is preferably retained, at least in part. The environment     flanks the nucleic acid sequence at least at one side and has a     sequence of at least 50 bp, preferably at least 500 bp, especially     preferably at least 1000 bp, very especially preferably at least     5000 bp, in length. A naturally occurring expression cassette—for     example the naturally occurring combination of the RacB promoter     with the corresponding RacB gene—becomes a transgenic expression     cassette when it is modified by non-natural, synthetic “artificial”     methods such as, for example, mutagenization. Such methods have been     described (U.S. Pat. No. 5,565,350; WO 00/15815; also see above).

The invention also relates to transgenic organisms transformed with at least one of the nucleic acid sequences according to the invention, expression cassette according to the invention or vector according to the invention, and to cells, cell cultures, tissues, parts—such as, for example, leaves, roots and the like in the case of plant organisms—or propagation material derived from such organisms. The term organism is to be understood in the broad sense and refers to prokaryotic and eukaryotic organisms, preferably bacteria, yeasts, fungi, animal organisms and plant organisms.

The following are preferred:

-   a) fungi such as Aspergillus, Eremothecium, Trichoderma, Ashbya,     Neurospora, Fusarium, Beauveria or other fungi described in Indian     Chem Eng. Section B. Vol 37, No. 1,2 (1995) on page 15, Table 6.     Especially preferred is the filamentous hemiascomycete Ashbya     gossypii or Eremothecium ashbyii, -   b) yeasts such as Candida, Saccharomyces, Hansenula or Pichia, with     Saccharomyces cerevisiae or Pichia pastoris (ATCC Accession     No. 201178) being especially preferred, -   c) plants in accordance with the above definition of “plants”, -   d) vertebrates and invertebrates. Especially preferred vertebrates     are nonhuman mammals such as in dog, cat, sheep, goat, chicken,     mouse, rat, cattle or horse. Preferred animal cells comprise CHO,     COS and HEK293 cells. Preferred invertebrates comprise insect cells     such as Drosophila S2 and Spodoptera Sf9 or Sf21 cells, -   e) prokaryotic organisms such as Gram-positive or Gram-negative     bacteria such as Acetobacter, Gluconobacter, Corynebacterium,     Brevibacterium, Bacillus, Clostridium, Cyanobacter, Escherichia     (mainly Escherichia coli), Serratia, Staphylococcus, Aerobacter,     Alcaligenes, Penicillium or Klebsiella.

Host or starting organisms which are preferred as transgenic organisms are mainly plants in accordance with the above definition. Included within the scope of the invention are all genera and species of higher and lower plants of the Plant Kingdom. Furthermore included are the mature plants, seed, shoots and seedlings, and parts, propagation material and cultures derived therefrom, for example cell cultures. Mature plants refers to plants at any developmental stage beyond that of the seedling. The term seedling refers to a young immature plant in an early developmental stage. Plants preferred as host organisms are in particular plants which can be used for the process according to the invention to obtain a pathogen resistance according to the criteria mentioned above. Very particularly preferred are monocotyledbnous plants, such as wheat, oats, millet, barley, rye, maize, rice, buckwheat, sorghum, triticale, spelt, linseed, sugar cane, as dicotyledonous crop plants, such as oil seed rape, canola, cress, Arabidopsis, cabbages, soya, alfalfa, pea, beans, peanut, potato, tobacco, tomato, eggplant, bell pepper, sunflower, Tagetes, lettuce, Calendula, melon, pumpkin/squash or zucchini.

The transgenic organisms can be generated with the above-described methods for the transformation or transfection of organisms.

The invention furthermore relates to the use of the transgenic organisms according to the invention and of the cells, cell cultures, parts—such as, for example, roots, leaves and the like in the case of transgenic plant organisms—derived from them, and to transgenic propagation material such as seeds or fruits, for the production of foodstuffs or feeding stuffs, pharmaceuticals or fine chemicals.

Furthermore preferred is a method for the recombinant production of pharmaceuticals or fine chemicals in host organisms, wherein a host organism is transformed with one of the above-described expression cassettes and this expression cassette comprises one or more structural genes which encode the desired fine chemical or catalyze the biosynthesis of the desired fine chemical, the transformed host organism is cultured, and the desired fine chemical is isolated from the culture medium. This method can be applied widely to fine chemicals such as enzymes, vitamins, amino acids, sugars, fatty acids, and natural and synthetic flavorings, aroma substances and colorants. Especially preferred is the production of tocopherols and tocotrienols and carotenoids. The transformed host organisms are cultured and the products are isolated from the host organisms or the culture medium by methods known to the skilled worker. The production of pharmaceuticals such as, for example, antibodies or vaccines, is described by Hood E E, Jilka J M. (1999) Curr Opin Biotechnol. 10(4):382-6; Ma J K, Vine N D. (1999) Curr Top Microbiol Immunol. 236:275-92. 1. SEQ ID NO: 1 Nucleic acid sequence encoding the barley (Hordeum vulgare) RacB protein. 2. SEQ ID NO: 2 Amino acid sequence encoding the barley (Hordeum vulgare) RacB protein. 3. SEQ ID NO: 3 Nucleic acid sequence encoding the rice (Oryza sativa) RacB protein. 4. SEQ ID NO: 4 Amino acid sequence encoding the rice (Oryza sativa) RacB protein. 5. SEQ ID NO: 5 Nucleic acid sequence encoding the maize (Zea mays) RacB protein. 6. SEQ ID NO: 6 Amino acid sequence encoding the maize (Zea mays) RacB protein. 7. SEQ ID NO: 7 Amino acid sequence encoding a dominant-negative variant of the RacB protein (Hordeum vulgare). 8. SEQ ID NO: 8 Amino acid sequence encoding a dominant-negative variant of the rice (Oryza sativa) RacB protein. 9. SEQ ID NO: 9 Amino acid sequence encoding a dominant-negative variant of the maize (Zea mays) RacB protein. 10. SEQ ID NO: 10 Oligonuceotide primer ONP-1 5′-GGATCCGATGAGCGCGTCCAGGTT-3′ 11. SEQ ID NO: 11 Oligonucleotide primer ONP-2 5′-GTCGACCTTCGCCCTTGTTCTTTGTC-3′ 12. SEQ ID NO: 12 RACE-RacB primer 5′-gtgggcacatagtcggtggggaaggt-3′ 13. SEQ ID NO: 13 GeneRacer ™ 5′ primer: 5′-CGACTGGAGCACGAGGACACTGA-3 14. SEQ ID NO: 14 GeneRacer ™ 5′ nested primer: 5′-GGACACTGACATGGACTGAAGGAGTA-3 15. SEQ ID NO: 15 RacB sense primer 5′-gttcatcaagtgcgtcaccgtg-3′ 16. SEQ ID NO: 16 RacB antisense primer 5′-ttagcttcctcagttcttccctg-3′ 17. SEQ ID NO: 17 BAS sense primer 5′-cgcgccgcagccgagtacgac-3′ 18. SEQ ID NO: 18 BAS antisense primer 5′-gtcacaaaaacacatgtaacc-3′ 19. SEQ ID NO: 19 OXLP sense primer 5′-ggccgacatgcattcaccag-3′ 20. SEQ ID NO: 20 OXLP antisense primer 5′-catctgatattgctgggtctg-3′ 21. SEQ ID NO: 21 UBI sense primer 5′-ccaagatgcagatcttcgtga-3′ 22. SEQ ID NO: 22 UBI antisense primer 5′-ttcgcgataggtaaaagagca-3′ 23. SEQ ID NO: 23 M13 fwd primer 5′-GTAAAACGACGGCCAGTG-3′ 24. SEQ ID NO: 24 M13 rev primer 5′-GGAAACAGCTATGACCATG-3′ 25. SEQ ID NO: 25 HvRop6 LEFT PRIMER 5′-GTGGAGGCGCGGCGAGA-3′ 26. SEQ ID NO: 26 HvRop6 RIGHT PRIMER 5′-CCATGCTTCATCTCCATAGTCA-3′ 27. SEQ ID NO: 27 HvRacD LEFT PRIMER 5′-ggatccCGATTCCATCAGGAAAGCAT-3′ 28. SEQ ID NO: 28 HvRacD RIGHT PRIMER 5′-gtcgacGCGAGACACTGCAAAACAAA-3′ 29. SEQ ID NO: 29 HvRop4 LEFT PRIMER 5′-GGATCCttctcgtccatttagccggc-3′ 30. SEQ ID NO: 30 HvRop4 RIGHT PRIMER 5′-GTCGACtgatcacttgaagcatgccag-3′ 31. SEQ ID NO: 31 RacB5′ BamHI Primer 5′-GGATCCGATGAGCGCGTCCAGGTT-3′ 32. SEQ ID NO: 32 RacB3′ SalI Primer 5′-GTCGACCTTCGCCCTTGTTCTTTGTC-3′ 33. SEQ ID NO: 33 V15 mutagenesis Primer 5′- ACCGTGGGGGACGTCGCCGTCGGCAAGAC-3′ 34. SEQ ID NO: 34 Nucleic acid sequence encoding the RacB homolog HvRop6 from barley (Hordeum vulgare). 35. SEQ ID NO: 35 Amino acid sequence encoding the RacB homolog HvRop6 from barley (Hordeum vulgare). 36. SEQ ID NO: 36 Nucleic acid sequence encoding the RacB homolog HvRacD from barley (Hordeum vulgare). 37. SEQ ID NO: 37 Amino acid sequence encoding the RacB homolog HvRacD from barley (Hordeum vulgare). 38. SEQ ID NO: 38 Nucleic acid sequence encoding the RacB homolog HvRop4 from barley (Hordeum vulgare). 39. SEQ ID NO: 39 Nucleic acid sequence encoding the RacB homolog HvRop4 from barley (Hordeum vulgare). 40. SEQ ID NO: 40 Nucleic acid sequence encoding the RacB homolog Zea mays ROP6 (GenBank Acc.-No.: AJ278665) 41. SEQ ID NO: 41 Amino acid sequence encoding the RacB homolog Zea mays ROP6 42. SEQ ID NO: 42 Nucleic acid sequence encoding the RacB homolog Oryza sativa subsp. japonica PACDP (RACD) (GenBank Acc.-No.: AF218381) 43. SEQ ID NO: 43 Amino acid sequence encoding the RacB homolog Oryza sativa subsp. japonica RACDP 44. SEQ ID NO: 44 Nucleic acid sequence encoding the RacB homolog Oryza sativa ROP4 (GenBank Acc.-No.: AF380335) 45. SEQ ID NO: 45 Amino acid sequence encoding the RacB homolog Oryza sativa ROP4 46. SEQ ID NO: 46 Nucleic acid sequence encoding the RacB homolog Zea mays RACA (GenBank Acc.-No.: AF126052) 47. SEQ ID NO: 47 Amino acid sequence encoding the RacB homolog Zea mays RACA 48. SEQ ID NO: 48 Nucleic acid sequence encoding an RacB homolog from Hordeum vulgare (GenBank Acc.-No.: BM816965) 49. SEQ ID NO: 49 Nucleic acid sequence encoding an RacB homolog from Arabidopsis thaliana (At3g51300) 50. SEQ ID NO: 50 Amino acid sequence encoding an RacB homolog from Arabidopsis thaliana (At3g51300) 51. SEQ ID NO: 51 Nucleic acid sequence encoding an RacB homolog from Arabidopsis thaliana (At2g17800) 52. SEQ ID NO: 52 Amino acid sequence encoding an RacB homolog from Arabidopsis thaliana (At2g17800) 53. SEQ ID NO: 53 Nucleic acid sequence encoding an RacB homolog from Arabidopsis thaliana (At4g35950) 54. SEQ ID NO: 54 Amino acid sequence encoding an RacB homolog from Arabidopsis thaliana (At4g35950) 55. SEQ ID NO: 55 Nucleic acid sequence encoding an RacB homolog from Arabidopsis thaliana (At1g75840) 56. SEQ ID NO: 56 Amino acid sequence encoding an RacB homolog from Arabidopsis thaliana (At1g75840) 57. SEQ ID NO: 57 Nucleic acid sequence encoding an RacB homolog from Arabidopsis thaliana (At4g35020) 58. SEQ ID NO: 58 Amino acid sequence encoding an RacB homolog from Arabidopsis thaliana (At4g35020) 59. SEQ ID NO: 59 Nucleic acid sequence encoding an RacB homolog from Arabidopsis thaliana (At1g20090) 60. SEQ ID NO: 60 Amino acid sequence encoding an RacB homolog from Arabidopsis thaliana (At1g20090) 61. SEQ ID NO: 61 Nucleic acid sequence encoding an RacB homolog from Arabidopsis thaliana (At5g45970) 62. SEQ ID NO: 62 Amino acid sequence encoding an RacB homolog from Arabidopsis thaliana (At5g45970) 63. SEQ ID NO: 63 Nucleic acid sequence encoding an RacB homolog from Arabidopsis thaliana (At3g48040) 64. SEQ ID NO: 64 Amino acid sequence encoding an RacB homolog from Arabidopsis thaliana (At3g48040) 65. SEQ ID NO: 65 Nucleic acid sequence encoding an RacB homolog from Arabidopsis thaliana (At5g62880) 66. SEQ ID NO: 66 Amino acid sequence encoding an RacB homolog from Arabidopsis thaliana (At5g62880) 67. SEQ ID NO: 67 Nucleic acid sequence encoding an RacB homolog from Arabidopsis thaliana (At4g28950) 68. SEQ ID NO: 68 Amino acid sequence encoding an RacB homolog from Arabidopsis thaliana (At4g28950) 69. SEQ ID NO: 79 Nucleic acid sequence encoding an RacB homolog from Arabidopsis thaliana (At2g44690) 70. SEQ ID NO: 70 Amino acid sequence encoding an RacB homolog from Arabidopsis thaliana (At2g44690) 71. SEQ ID NO: 71 Oligonucleotide primer Fra 186 5′-ATGAGCGCGTCCAGGTTCATA-3′ 72. SEQ ID NO: 72 Oligonucleotide primer Fra 187 5′-ATCAAACACGCCCTTCACGTT-3′ 73. SEQ ID NO: 73 Transgenic expression vector pSUN3NIT_AtRacB_s for expression of Arbidopsis thalianan RacB in sense orientation 74. SEQ ID NO: 74 Transgenic expression vector pSUN3NIT_AtRacB_as for expression of Arbidopsis thalianan RacB in antisense orientation 75. SEQ ID NO: 75 Transgenic expression vector pSUN3NIT_HvRacB_s for expression of a barley RacB fragment in sense orientation 76. SEQ ID NO: 76 Transgenic expression vector pSUN3NIT_HvRacB_as for expression of a barley RacB fragment in antisense orientation

FIGURES

1. FIG. 1: Alignment of the amino acid sequences of barley RacB, rice RacB, maize RacB, and human Rac1 and Rac2 proteins.

Regions shaded in gray show the position of the G1 element (GXXXXGKS/T; amino acid 13 to 20), of the G2 effector region (amino acid 29 to 45), of the G3 element (LWDTAGQ; amino acid 58 to 64), of the G4 element (TKXD; amino acid 118 to 121), of the G5 element (EXS) and of the C-terminal isoprenylation motif (CXXX, Hassanain H H et al. (2000) Biochem Biophys Res Commun. 272(3):783-8.). Hyphens indicate sequence gaps. Asterisks denote amino acids which are identical in all homologs. Amino acids which differ between barley on the one hand and maize and rice on the other hand are shown white against black. The position which is advantageously modified to obtain a dominant-negative RacB variant is marked by a black triangle above the sequence.

2. FIG. 2: Expression of RacB in epidermal tissue

RT-PCR of RNA from the barley lines Pallas and BCPMla12 (P10) 24 h post-inoculation (“hai” hours after inoculation”) with BghA6. To extract the RNA, strips of the abaxial epidermis (E, from inoculated locations of leaves) were removed from the mesophyll and the adaxial epidermis (M). Ubiquitin 1 (Ubi) acted as marker for tissue-unspecific expression, OXLP as positive control for gene expression in the epidermis, and Bas as positive control for gene expression in mesophyll cells. The RT-PCR was carried out over 25 amplification cycles as described hereinbelow. RT-PCR products were denatured in the gel, blotted and detected by means of antisense RNA probes under stringent conditions.

3. FIG. 3: RacB is expressed constitutively in various resistant barley lines.

RNA was isolated from the variety Ingrid (Mlo, Ror1, Bgh-susceptible), BCIngrid-mlo5 (mlo5, Ror1, Bgh-resistant) and A89 (mlo5, ror1, moderately susceptible to BghA6) immediately prior to inoculation (0 Ø) or 8, 15 or 24 h post-inoculation with Bgh and 24 h thereafter from noninoculated control plants (24 Ø). Ubiquitin 1 (Ubi) was used as marker for constitutive expression, OXLP as positive control for Bgh-induced gene expression in the epidermal layer. OXLP expression was detected via Northern blot. The RT-PCR for RacB and Ubi was carried out as described over 25 amplification cycles. The PCR products were denatured in the gel, blotted and detected by means of antisense RNA samples under stringent conditions.

4. FIG. 4: “RNA interference” with RacB-dsRNA reduces the penetration efficacy of barley powdery mildew BghA6 in barley.

The relative penetration efficacy (RPE) was determined in six individual experiments with inoculation with Bgh from barley cv. Pallas. The RPE was calculated as the difference between the penetration efficacy of cells transformed with RacB-dsRNA and the penetration efficacy of cells transformed with control dsRNA (here: average penetration efficacy 57%). The RPE percentage (%-RPE) is calculated from the RPE minus 1, multiplied by 100. ${RPE} = \frac{\left\lbrack {{PE}\quad{of}\quad{cells}\quad{transformed}\quad{with}\quad{RacB}\text{-}{dsRNA}} \right\rbrack}{\left\lbrack {{PE}\quad{of}\quad{cells}\quad{transformed}\quad{with}\quad{control}\quad{dsRNA}} \right\rbrack}$ %-RPE = 100 * (RPE-1)

The black columns represent the %-RPE upon evaluation of at least 100 interaction sites for in each case one independent experiment. The white column represents the average %-RPE of the experiments with the RacB-dsRNA (“RACB-dsRNA”). The error bar indicates the standard error.

“control” represents the parallel experiments with a control dsRNA.

In cells which had been bombarded with RacB-dsRNA, the %-RPE was markedly reduced in comparison with cells which had been bombarded with a control dsRNA (TR: human thyroid receptor dsRNA).

5. FIG. 5: Effect of the genetic background on RacB function

The %-RPE was studied in 5 independent experiments by inoculating barley cv. Pallas, Ingrid or A89, which had previously been transformed with RacB-dsRNA, with BghA6.

The %-RPE is markedly reduced in Pallas (Mlo Ror1, black bars, experiments 1 and 2) or Ingrid (Mlo Ror1, black bars, experiments 3, 4 and 5). The %-RPE of the susceptible mutant A89 (mlo5 ror1, black bars, experiments 1 to 5), however, was not reduced. White bars indicate the mean, error bars the standard error.

6. FIG. 6: Overexpression of a constitutively active RacB mutant in barley cv. Pallas

A constitutively active mutant of barley RACB (exchange G->V in position 15; RacB-V15) was transiently overexpressed in the barley variety Pallas in 5 independent experiments using the expression construct pGY-RacBV15. For comparison, corresponding experiments were carried out using the vector alone, without RacB insert (pGY).

The expression of a constitutive RacB mutant results in significantly higher susceptibility to pathogen attack by mildew of barley, compared to the controls (FIG. 6-A). In all cases, the relative susceptibility to the fungal pathogen is increased (FIG. 6-B). These results, too, demonstrate the key function of racB in the defense of pathogens.

7. FIG. 7: Plasmid map for expression vector pGY-1 (Schweizer P et al. (1999) Mol Plant Microbe Interact 12: 647-54; Shinshi H et al. (1990) Plant Mol Biol 14:357-368).

EXAMPLES

General Methods:

The chemical synthesis of oligonucleotides can be effected, for example, in the known fashion using the phosphoamidite method (Voet, Voet, 2nd Edition, Wiley Press New York, pages 896-897). The cloning steps carried out for the purposes of the present invention such as, for example, restriction cleavages, agarose gel electrophoresis, purification of DNA fragments, transfer of nucleic acids to nitrocellulose and nylon membranes, linking DNA fragments, transformation of E. coli cells, growing bacteria, multiplying phages and sequence analysis of recombinant DNA, are carried out as described by Sambrook et al. (1989) Cold Spring Harbor Laboratory Press; ISBN 0-87969-309-6. The sequencing of recombinant DNA molecules is carried out with an MWG-Licor laser fluorescence DNA sequencer following the method of Sanger (Sanger et al. (1977) Proc Natl Acad Sci USA 74:5463-5467).

Example 1 Plants, Pathogens and Inoculation

The barley variety Ingrid is from James McKey, University of Uppsala, Sweden. The variety Pallas and backcrossed line BCIngrid-mlo5 was donated by Lisa Munk, Department of Plant Pathology, Royal Veterinary and Agricultural University, Copenhagen, Denmark. Its production has been described (Kølster P et al. (1986) Crop Sci 26: 903-907). Line A89 was provided by Paul Schulze-Lefert (Max-Plank-Institut für Züchtungsforschung, Cologne, Germany).

Unless otherwise specified, the seed which had been pregerminated on moist filter paper for 12 to 36 hours in the dark was sown along the edge of a square pot (8×8 cm; 5 kernels per pot) in Fruhstorfer soil, type P, covered with soil and watered regularly with tap water. All of the plants were cultured in controlled-environment cabinets or chambers for 5 to 8 days at 16 to 18° C., 50 to 60% relative atmospheric humidity and a 16-hr-light/8-hr-dark rhythm at 3000 or 5000 lux (photon flow density 50 and 60 μmols-¹m-², respectively) and used in the experiments during the seedling stage. In experiments in which applications to the primary leaves were carried out, the latter were developed fully.

Before the transient transfection experiments were carried out, the plants were grown in controlled-environment cabinets or chambers at a daytime temperature of 24° C., a nighttime temperature of 20° C., 50 to 60% relative atmospheric humidity and a 16-hr light/8-hr-dark rhythm at 30 000 lux.

Barley powdery mildew Blumeria graminis (DC) Speer f.sp. hordei Em. Marchal race A6 (Wiberg A (1974) Hereditas 77: 89-148) (BghA6) was used for the inoculation of barley plants. The fungus was provided by the Department of Biometry, JLU Gieβen. Inoculum was grown in controlled-environment cabinets under identical conditions to those described above for the plants by transferring the conidia of infected plant material at a rate of 100 conidia/mm² to 7-day-old barley plants cv. Golden Promise, which were grown regularly.

The inoculation with BghA6 was carried out using 7-day-old seedlings by shaking off the conidia of already infected plants in an inoculation tower at a rate of approx. 100 conidia/mm² (unless otherwise specified).

Example 2 RNA Extraction

Total RNA was extracted from 8 to 10 primary leaf segments (length 5 cm) by means of “RNA extraction buffer” (AGS, Heidelberg, Germany).

To this end, the central primary leaf segments 5 cm in length were harvested and homogenized in liquid nitrogen in mortars. The homogenate was stored at −70° C. until the RNA was extracted.

Total RNA was extracted from the deep-frozen leaf material with the aid of an RNA extraction kit (AGS, Heidelberg). To this end, 200 mg of the deep-frozen leaf material were covered with 1.7 ml RNA extraction buffer (AGS) in a microcentrifuge tube (2 ml) and immediately mixed thoroughly. After addition of 200 μl of chloroform, the mixture was again mixed thoroughly and shaken for 45 minutes on a horizontal shaker at 200 rpm at room temperature. To separate the phases, the tubes were subsequently centrifuged for 15 minutes at 20 000 g and 4° C., and the upper, aqueous phase was transferred into a fresh microcentrifuge tube, while the bottom phase was discarded. The aqueous phase was repurified with 900 μl of chloroform by homogenizing for 10 seconds and recentrifuging (see above) and removing the aqueous phase (3 times). Then, 850 μl of 2-propanol were added and the mixture was homogenized and placed on ice for 30 to 60 minutes in order to precipitate the RNA. Thereafter, the mixture was centrifuged for 20 minutes (see above), the supernatant was carefully decanted off, 2 ml of 70% strength ethanol (−20° C.) were pipetted in, and the mixture was mixed and recentrifuged for 10 minutes.

Then, the supernatant was again decanted off, and the pellet was carefully freed from residual fluid, using a pipette, and then dried in a stream of clean air in a clean bench. Then, the RNA was dissolved in 50 μl of DEPC water on ice, mixed and centrifuged for 5 minutes (see above). 40 μl of the supernatant, constituting the RNA solution, were transferred into a fresh microcentrifuge tube and stored at −70° C.

The RNA concentration was determined photometrically. To this end, the RNA solution was diluted 1:99 (v/v) with distilled water, and the absorption was measured at 260 nm (Beckman Photometer DU 7400); (E₂₆₀ 1 at 40 μg RNA/ml). The concentrations of the RNA solutions were subsequently adjusted to 1 μg/μl with DEPC water to match the calculated RNA contents and verified in an agarose gel.

To verify the RNA concentrations in a horizontal agarose gel (1% agarose in 1×MOPS buffer with 0.2 μg/ml ethidium bromide), 1 μl of RNA solution was treated with 1 μl of 10×MOPS, 1 μl of color marker and 7 μl of DEPC water, separated according to size in 1×MOPS running buffer over 1.5 hours at a voltage of 120 V in the gel, and photographed under UV light. Any differences in concentration of the RNA extracts were adjusted with DEPC water, and the adjustment was rechecked in the gel.

Example 3 Cloning the Barley RacB cDNA Sequence

The cDNA fragments required for isolating the HvRacB cDNA, cloning it, sequencing it and generating probes were obtained by means of RT-PCR using the “One Step RT-PCR Kit” (Life Technologies, Karlsruhe, Germany or Qiagen, Hilden, Germany). To this end, total RNA from barley seedlings was used as template.

The RNA was isolated from Pallas 3, 5 and 0.7 days after germination. Moreover, RNA was isolated from Pallas and the backcrossed lines with mlo5, Mlg or Mla12 1, 2 and 5 days after inoculation with BghA6 on day 7 after germination. The following primers are used for the RT-PCR: ONP-1 5′-GGATCCGATGAGCGCGTCCAGGTT-3′ (SEQ ID NO: 10) and ONP-2 5′-GTCGACCTTCGCCCTTGTTCTTTGTC-3′ (SEQ ID NO: 11) 1000 ng of total RNA, 0.4 mM dNTPs, in each case 0.6 mM OPN-1 and OPN-2 primer, 10 μl of RNase inhibitor and 1 μl of enzyme mix in 1×RT buffer (One Step RT-PCR Kit, Qiagen, Hilden) were employed for each reaction (25 μl batch).

The following temperature program is used (PTC-100TM model 96V; MJ Research, Inc., Watertown, Mass.):

-   -   1 cycle of 30 min at 50° C.     -   1 cycle of 150 sec at 94° C.     -   30 cycles of 45 sec at 94° C., 1 min at 55° C. and 2 min at 72°         C.     -   1 cycle of 7 min at 72° C.

The PCR product was separated by 2% w/v agarose gel electrophoresis. This gave an RT-PCR product of in total 642 bp which was composed of the RacB sequence (SEQ ID NO: 1) and terminal sequences encoding restriction endonuclease restriction sites. The fragment encodes a 591 bp open reading frame encoding a polypeptide of 197 amino acids. The corresponding cDNA was isolated from an agarose gel and cloned into vector pGEM-T (Promega, Mannheim, Germany) by means of T-overhang ligation. The cDNAs were sequenced starting from the plasmid DNA using the “Thermo Sequenase Fluorescent Labeled Primer Cycle Sequencing Kit” (Amersham, Freiburg, Germany).

Since a primer has been deduced from the rice RacB sequence as starting primer OPN-1 (GenBank Acc. No.: AF250327), this region (i.e. the 5′-end) of the barley RacB cDNA was reverified by means of RACE technology using the “GeneRacer Kit” (INVITROGENE Life Technologies). To this end, 100 ng of poly-A mRNA, 1 μl of 10×CIP buffer, 10 units of RNAse inhibitor, 10 units of CIP (“calf intestinal phosphatase”) and DEPC-treated water were treated for 1 hour at 50° C. in a total volume of 10 μl. To precipitate the RNA, a further 90 μl of DEPC water and 100 μl of phenol:chloroform were added and the mixture was mixed thoroughly for approximately 30 seconds. After centrifugation for 5 minutes at 20 000 g, the top phase was treated with 2 μl of 10 mg/ml mussel glycogen, 10 μl of 3 M sodium acetate (pH 5.2) in a fresh micro reaction vessel. 220 μl of 95% ethanol were added and the mixture was incubated on ice. The RNA was subsequently precipitated by centrifugation for 20 minutes at 20 000 g and 4° C. The supernatant was discarded, 500 μl of 75% ethanol were added, and the mixture was vortexed briefly and recentrifuged for 2 minutes (20 000 g). Again, the supernatant was discarded, and the precipitate was dried in the air for 0.2 minutes at room temperature and subsequently suspended in 6 μl of DEPC water. mRNA CAP structures were removed by adding 1 μl of 10× TAP buffer, 10 units of RNAsin and 1 unit of TAP (tobacco acid pyrophosphatase). The mixture was incubated for 1 h at 37° C. and subsequently cooled on ice. Again, the RNA was precipitated as described above and transferred into a reaction vessel with 0.25 μg of GeneRacer oligonucleotide primer. The oligonucleotide primer was resuspended in the RNA solution, and the mixture was incubated for 5 minutes at 70° C. and then ice-cooled. 1 μl of 10× ligase buffer, 10 mM ATP, 1 unit of RNAsin and 5 units of T4 RNA ligase were added, and the batch was incubated for 1 h at 37° C. Again, the RNA was precipitated as described above and resuspended in 13 μl of DEPC water. 10 pmol of oligo-dT primer were added to the RNA, and the mixture was immediately heated at 70° C. and again cooled on ice. 1 μl of each dNTP solution (25 mM), 2 μl of 10× RT buffer, 5 u (1 μl) of AMV reverse transcriptase and 20 units of RNAsin were added, and the reaction solution was incubated for 1 hour at 42° C. and subsequently for 15 minutes at 85° C. The first-strand cDNA thus prepared was stored at −20° C.

The following primer was used to amplify the 5′-cDNA ends: RACE RacB primer: 5′-gtgggcacatagtcggtggggaaggt-3′ (SEQ ID NO: 12) GeneRacer ™ 5′-primer: 5′-CGACTGGAGCACGAGGACACTGA-3 (SEQ ID NO: 13) GeneRacer ™ 5′-nested primer: 5′-GGACACTGACATGGACTGAAGGAGTA-3 (SEQ ID NO: 14)

The batch (total volume 25 μl) was composed as follows:

-   -   1 μl primer RACE-RacB (5 pmol/μl),     -   0.5 μl GeneRacer 5′-primer (10 pmol/μl)     -   2.5 μl 10× buffer Qiagen,     -   2.5 μl dNTPs (2 mM)     -   0.5 μl cDNA     -   0.2 μl QiagenTAG (5 u/μl)     -   17.8 μl H2O

The PCR conditions were:

-   -   94° C. denaturation for 5 minutes     -   5 cycles of 30 seconds at 70° C. (annealing),         -   1 min at 72° C. (extension),         -   30 seconds at 94° C. (denaturation)     -   5 cycles of 30 seconds at 68° C. (annealing),         -   1 min at 72° C. (extension),         -   30 seconds at 94° C. (denaturation)     -   28 cycles of 30 seconds at 66° C. (annealing),         -   1 min at 72° C. (extension),         -   30 seconds at 94° C. (denaturation)     -   72° C. final extension for 10 minutes     -   4° C. cooling until further use

The PCR gave a product of approx. 400 bp product. Starting from this product, a nested PCR with the RacB-specific oligonucleotide primer and the “GeneRacer nested 5′-primer” was carried out:

-   -   94° C. denaturation for 5 minutes     -   30 cycles of 30 sec at 64° C. (annealing),         -   1 min at 72° C. (extension),         -   30 sec at 94° C. (denaturation)     -   72° C. final extension for 10 minutes     -   4° C. cooling until further use

The PCR product obtained was isolated via a gel, extracted from the gel, cloned into PGEM-T by means of T-overhang ligation, and sequenced. The sequence in the region of the primer OPN-1 was absolutely identical to the sequence of rice racB, so that no point mutations could be generated by means of primers. Thus, the sequence shown under SEQ ID NO: 1 is identical to the barley RacB sequence.

Example 4 Reverse Transcription Polymerase Chain Reaction (RT-PCR)

The “One Step RT-PCR Kit” (Qiagen, Hilden, Germany) was used for the semi-quantitative RT-PCR. In doing so, RNA (prepared as above) was first translated into cDNA (reverse transcription) and the sought cDNA was amplified in a subsequent PCR reaction using specific primers. To estimate the initial amount of template RNA, the amplification was interrupted during the exponential phase in order to reflect differences in the target RNA. The PCR products were separated by means of an agarose gel, denatured, blotted onto nylon membranes, and detected with specific non-radiolabeled probes under stringent standard conditions. Hybridization, wash steps and immunodetection were carried out as described under “Northern blot”.

The following components were combined for the individual reactions (25 μl batch) using the “One Step RT-PCR Kit” (Qiagen, Hilden, Germany):

-   -   1000 ng total RNA of a specific sample     -   0.4 mM dNTPs     -   0.6 μM of each sense and antisense primer     -   0.1 μl RNase inhibitor     -   1 μl enzyme mix in 1×RT buffer

cDNA synthesis (reverse transcription) was carried out for 30 minutes at 50° C. The reverse transcriptase was subsequently inactivated for 15 minutes at 95° C., which simultaneously causes activation of DNA polymerase and denaturation of cDNA. A PCR was subsequently carried out with the following program:

-   -   denaturation for 1 minute at 94° C.     -   25 cycles of 1 minute at 54° C. primer annealing         -   1 minute at 72° C. primer extension         -   10 minutes at 72° C. completion of the DNA duplexes     -   then: termination of the reaction at 4° C.

The PCR products were separated in a 1×TBE agarose gel using ethidium bromide.

The following oligonucleotide primer pairs were used for the amplifications in the individual batches:

a) amplification of a 387 bp fragment of the barley RacB cDNA RacB sense 5′-gttcatcaagtgcgtcaccgtg-3′ (SEQ ID NO: 15) RacB antisense 5′-ttagcttcctcagttcttccctg-3′ (SEQ ID NO: 16)

b) amplification of a 674 bp fragment of barley BAS cDNA (GenBank Acc. No. Z34917) BAS 5′-cgcgccgcagccgagtacgac-3′ (SEQ ID NO: 17) sense BAS 5′-gtcacaaaaacacatgtaacc-3′ (SEQ ID NO: 18) anti- sense

c) amplification of a 506 bp OXLP cDNA fragment (GenBank Acc. No. X93171) OXLP 5′-ggccgacatgcattcaccag-3′ (SEQ ID NO: 19) sense OXLP 5′-catctgatattgctgggtctg-3′ (SEQ ID NO: 20) anti- sense

d) amplification of a 513 bp Ubi cDNA fragment (GenBank accession M60175) UBI 5′-ccaagatgcagatcttcgtga-3′ (SEQ ID NO: 21) sense UBI 5′-ttcgcgataggtaaaagagca-3′ (SEQ ID NO: 22) anti- sense

All of the fragments obtained were additionally ligated into the vector PGEM-T by means of T-overhang ligation and were used as starting plasmids for the generation of probes (for example for Northern blots) or dsRNA. The individual constructs were named pGEMT-RAC1, PGEMT-BAS, pGEMT-OXLP, pGEMT-UBI.

Example 5 Northern Blot Analysis

To prepare the Northern blotting, the RNA was separated in an agarose gel under denaturing conditions. To this end, part of the RNA solution (corresponding to 5 μg of RNA) was mixed with an identical volume of sample buffer (with ethidium bromide), denatured for 5 minutes at 94° C., placed on ice for 5 minutes, centrifuged briefly and applied to the gel. The 1×MOPS gel (1.5% agarose, ultra pure grade) contained 5 percent by volume of concentrated formaldehyde solution (36.5% [v/v]). The RNA was separated for 2 hours at 100 V and subsequently blotted.

Northern blotting was done as an upward capillary RNA transfer. To this end, the gel was first agitated gently for 30 minutes in 25 mM sodium hydrogen/dihydrogen phosphate buffer (pH 6.5) and cut to size. A piece of Whatman paper was prepared in such a way that it rested on a horizontal support and extended on 2 sides into a trough with 25 mM sodium hydrogen/dihydrogen phosphate buffer (pH 6.5). This piece of paper was covered with the gel, uncovered parts of the piece of Whatman paper being covered with a plastic film. The gel was then covered with a positively charged nylon membrane (Boehringer-Mannheim), avoiding air bubbles, whereupon the membrane was recovered to a height of approximately 5 cm with a stack of blotting paper. The blotting paper was additionally weighed down with a sheet of glass and with a 100 g weight. Blotting was carried out overnight at room temperature. The membrane was rinsed briefly in twice-distilled water and irradiated with UV light in a crosslinking apparatus (Biorad) with a light energy of 125 mJ in order to immobilize the RNA. The uniformity of the RNA transfer to the membrane was checked on a UV light bench.

To detect barley mRNA, 10 μg of total RNA from each sample were resolved in an agarose gel and blotted onto a positively charged nylon membrane by capillary transfer. Detection was effected using the DIG system.

Probe preparation: Digogygenin—or fluorescein-labeled RNA probes were prepared for hybridization with the mRNAS to be detected. The probes were generated by in-vitro transcription of a PCR product by means of a T7 or SP6 RNA polymerase, using labeled UTPs. The template for the PCR-aided amplification was provided by the above-described plasmid vectors pGEMT-RAC1, pGEMT-BAS, pGEMT-OXLP, PGEMT-UBI.

Depending on the orientation of the insert, different RNA polymerases were used for generating the antisense strand. T7 RNA polymerase was used for PGEMT-BAS and PGEMT-OXLP, while SP6—RNA polymerase was used for pGEMT-RAC1 and pGEMT-UBI.

The insert of the individual vector was amplified via PCR using flanking standard primers (M13 fwd and rev). The reaction proceeded with the following end concentrations in a total volume of 50 μl of PCR buffer (Silverstar): M13-fwd: 5′-GTAAAACGACGGCCAGTG-3′ (SEQ ID NO: 23) M13-rev: 5′-GGAAACAGCTATGACCATG-3′ (SEQ ID NO: 24)

-   -   10% dimethyl sulfoxide (v/v)     -   2 ng/μl of each primer (M13 forward and reversed)     -   1.5 mM MgCl₂,     -   0.2 mM dNTPs,     -   4 units Taq polymerase (Silverstar),     -   2 ng/μl plasmid DNA.

The amplification was carried out in a Thermocycler (Perkin-Elmar 2400) with the following temperature program:

-   -   94° C. denaturing for 3 minutes     -   30 cycles of 30 seconds at 94° C. (denaturing)         -   30 seconds at 58° C. (annealing),         -   1.2 minutes at. 72° C. (extension),     -   72° C. final extension for 5 minutes     -   4° C. cooling until further use

The success of the reaction was verified in a 1% agarose gel. The products were subsequently purified using a “High Pure PCR-Product Purification Kit” (Boehringer-Mannheim). This gave approximately 40 μl of column eluate, which was again verified in the gel and stored at −20° C.

The RNA polymerization, the hybridization and the immunodetection were carried out largely following the kit manufacturer's instructions regarding the nonradioactive RNA detection (DIG System User's Guide, DIG-Luminescence detection Kit, Boehringer-Mannheim, Kogel et al. (1994) Plant Physiol 106:1264-1277). 4 μl of purified PCR product were treated with 2 μl of transcription buffer, 2 μl of NTP labeling mix, 2 μl of NTP mix and 10 μl of DEPC water. Then, 2 μl of the T7 RNA polymerase solution were pipetted in. The reaction was then carried out for 2 hours at 37° C. and then made up to 100 μl with DEPC water. The RNA probe was detected in an ethidium bromide gel and stored at −20° C.

To prepare the hybridization, the membranes were first agitated gently for 1 hour at 68° C. in 2×SSC (salt, sodium citrate), 0.1% SDS buffer (sodium dodecyl sulfate), the buffer being renewed twice or 3 times. The membranes were subsequently applied to the internal wall of hybridization tubes preheated at 68° C. and incubated for 30 minutes with 10 ml of Dig-Easy hybridization buffer in a preheated hybridization oven. In the meantime, 10 μl of probe solution were denatured for 5 minutes at 94° C. in 80 μl of hybridization buffer, and the mixture was subsequently placed on ice and centrifuged briefly. For the hybridization, the probe was then transferred into 10 ml of hybridization buffer at a temperature of 68° C., and the buffer in the hybridization tube was replaced by this probe buffer. Hybridization was then carried out overnight, likewise at 68° C.

Prior to the immunodetection of RNA-RNA hybrids, the blots were washed twice under stringent conditions for in each case 20 minutes in 0.1% (w/v) SDS, 0.1×SSC at 68° C.

For the immunodetection, the blots were first agitated twice for 5 minutes in 2×SSC, 0.1% SDS at RT. 2 stringent wash steps were subsequently carried out for in each case 15 minutes at 68° C. in 0.1×SSC, 0.1% SDS. The solution was then replaced by wash buffer without Tween. The reaction mix was shaken for 1 minute and the solution was exchanged for blocking reagent. After a further 30 minutes' shaking, 10 μl of anti-fluorescein antibody solution were added, and shaking was continued for 60 minutes. This was followed by two 15-minute wash steps in Tween-containing wash buffer. The membrane was subsequently equilibrated for 2 minutes in substrate buffer and, after being left to drain, transferred to a sheet of acetate paper. A mixture of 20 μl CDP-Star™ and 2 ml of substrate buffer was then divided uniformly on the “RNA side” of the membrane. The membrane was subsequently covered with a second sheet of acetate paper and the edges were heat-sealed to provide a water-tight seal, avoiding air bubbles. In a dark room, the membrane was then covered for 10 minutes with an X-ray film and the film was subsequently developed. The exposure time was varied as a function of the luminescence reaction.

Unless otherwise specified, the solutions were part of the kit as delivered (DIG-Luminescence detection Kit, Boehringer-Mannheim). All the others were prepared from the following stock solutions by dilution with autoclaved distilled water. Unless otherwise specified, all the stock solutions were made with DEPC (like DEPC water) and subsequently autoclaved.

-   -   DEPC water: distilled water is treated overnight at 37° C. with         diethyl pyrocarbonate (DEPC, 0.1%, w/v) and subsequently         autoclaved.     -   10×MOPS buffer: 0.2 M MOPS (morpholine-3-propanesulfonic acic),         0.05 M sodium acetate, 0.01 M EDTA, pH brought to 7.0 with 10 M         NaOH.     -   20×SSC (sodium chloride/sodium citrate, salt/sodium citrate): 3         M NaClo, 0.3 M trisodium citrate×2H₂O, pH brought to 7.0 with 4         M HCl.     -   1% SDS (sodium dodecyl sulfate) sodium dodecyl sulfate (w/v),         without DEPC.     -   RNA sample buffer: 760 μl formamide, 260 μl formaldehyde, 100 μl         ethidium bromide (10 mg/ml), 80 μl glycerol, 80 μl bromophenol         blue (saturated), 160 μl 10×MOPS, 100 μl water.     -   10×wash buffer without Tween: 1.0 M maleic acid, 1.5 M NaCl;         without DEPC, bring to pH 7.5 with NaOH (solid, approx. 77 g)         and 10 M NaOH.     -   Tween-containing wash buffer: made by adding Tween to wash         buffer without Tween (0.3%, v/v).     -   10×blocking reagent: suspend 50 g of blocking powder         (Boehringer-Mannheim) in 500 ml of wash buffer without Tween.     -   Substrate buffer: bring 100 mM Tris         (trishydroxymethylaminomethane), 150 mM NaCl to pH 9.5 with 4 M         HCl.     -   10×color marker: 50% glycerol (v/v), 1.0 mM EDTA pH 8.0, 0.25%         bromophenol blue (w/v), 0.25% xylene cyanole (w/v).

Example 6 In Vitro Synthesis of the RacB dsRNA

All of the plasmids (pGEMT-RAC1, pGEMT-BAS, pGEMT-OXLP, pGEMT-UBI) which were employed for in-vitro transcription comprise the T7 and SP6 promoters (pGEM-T, Promega) at the respective ends of the nucleic acid sequence inserted, which makes possible the synthesis of sense or antisense RNA. The plasmids can be linearized with suitable restriction enzymes in order to ensure correct transcription of the nucleic acid sequence inserted and to prevent reading being continued into vectorial sequences.

To this end, 10 μg of plasmid DNA were cleaved with in each case at the side of the insert which was located distally from the promoter. The cleaved plasmids are extracted in 200 μl of water with an identical volume of phenol/chloroform/isoamyl alcohol, transferred into a new Eppendorf reaction vessel (RNAse-free) and centrifuged for 5 minutes at 20 000 g. 180 μl of the plasmid solution were treated with 420 μl of ethanol, and the mixture was placed on ice and subsequently precipitated by centrifugation for 30 minutes at 20 000 g and −4° C. The precipitate was taken up in 10 μl of TE buffer.

To prepare the RacB dsRNA, the plasmid pGEMT-Rac1 was digested with SpeI, and sense RNA was transcribed using T7 RNA polymerase.

Furthermore, pGEMT-Rac1 was digested with NcoI, and antisense RNA was transcribed using SP6 RNA polymerase. RNA polymerases were obtained from Roche Molecular Biology, Mannheim, Germany.

Each transcription reaction contained the following in a volume of 40 μl:

-   -   2 μl of linearized plasmid DNA (1 μg)     -   2 μl of NTPs (25 mM) (1.25 mM of each NTP)     -   4 μl of 10× reaction buffer (Roche Molecular Biology),     -   1 μl of RNAsin RNAsin (27 units; Roche Molecular Biology),     -   2 μl of RNA polymerase (40 units)     -   29 μl of DEPC water

Following incubation for 2 hours at 37° C., part of the reactions from the transcription of the sense and antisense strand, respectively, were mixed, denatured for 5 minutes at 95° C. and subsequently hybridized (annealed) by cooling to a final temperature of 37° C. over 30 minutes. Alternatively, it is also possible first to denature the mixture of sense and antisense strand and then to cool it for 30 minutes at −20° C. The protein precipitate which formed during denaturing and hybridization was removed by briefly centrifuging the reaction at 20 800 g, and the supernatant was used directly for coating tungsten particles (see hereinbelow). For analysis, 1 μl of each RNA strand and of the dsRNA were resolved on a nondenaturing agarose gel. Successful hybridization manifested itself by a band shift toward higher molecular weight in comparison with the single strands.

4 μl of the dsRNA were ethanol-precipitated (by adding 6 μl of water, 1 μl of 3M sodium acetate solution and 25 μl of ethanol, and centrifugation for at least 5 minutes at 20 000 g and 4° C.) and the pellet was resuspended in 500 μl of water. The absorption spectrum between 230 and 300 nm was measured or the absorption at 280 and 260 nm was determined in order to determine the purity and concentration of the dsRNA. As a rule, 80 to 100 μl of dsRNA with an OD₂₆₀/OD₂₈₀ ratio of 1.80 to 1.95 were obtained. Digestion with DNase I can optionally be carried out, but has no significant effect on the results which follow.

The control dsRNA used was the human thyroid receptor dsRNA (starting vector pT7betaSal (Norman C et al. (1988) Cell 55(6):989-1003), provided by Dr. Baniahmad, Department of Genetics, Gieβen, Germany; the sequence of the insert is described under the GenBank Acc. No.: NM_(—)000461). To generate the sense RNA, the plasmid was digested with PvuII, to generate the antisense RNA, it was digested with HindIII, and the RNA was then transcribed with T7 and SP6 RNA polymerase, respectively. The individual process steps for generating the control dsRNA are carried out analogously to those described above for the RacB dsRNA.

Example 7 Transient Transformation, RNAi, and Evaluation of the Development of the Fungal Pathogen

Barley cv. Pallas leaf segments were transformed with an RacB dsRNA together with a GFP expression vector. The leaves were subsequently inoculated with Bgh, and the result was analyzed after 48 hours by light and fluorescence microscopy. The penetration into GFP-expressing cells was assessed by detecting haustoria in live cells and by assessing the fungal development on precisely these cells. In all six experiments, bombardment of barley cv. Pallas with RacB dsRNA resulted in a reduced number of successfully Bgh-penetrated cells in comparison with cells which had been bombarded with a foreign control dsRNA (human thyroid hormone receptor dsRNA, TR). The resistance-inducing effect of the RacB dsRNA caused an average reduction in Bgh penetration efficacy by 44% (FIG. 4).

A method was employed for the transient transformation which had already been described for the biolistic introduction of dsRNA into epidermal cells of barley leaves (Schweizer P et al. (1999) Mol Plant Microbe Interact 12:647-54; Schweizer P et al. (2000) Plant J 2000 24: 895-903). Tungsten particles with a diameter of 1.1 μm (particle density 25 mg/ml) were coated with dsRNA (preparation see above) together with plasmid DNA of the vector pGFP (GFP under the control of the CaMV ³⁵S promoter) as transformation marker. For each bombardment, the following amounts of dsRNA and reporter plasmid were used for coating: 1 μg of pGFP and 2 μg of dsRNA. Double-stranded RNA was synthesized in vitro by annealing sense and antisense RNA (see above).

To prepare microcarriers, 55 mg of tungsten particles (M 17, diameter 1.1 μm; Bio-Rad, Munich) were washed twice with 1 ml of autoclaved distilled water and once with 1 ml of absolute ethanol, dried and taken up in 1 ml of 50% strength glycerol (approx. 50 mg/ml stock solution). The solution was diluted to 25 mg/ml with 50% strength glycerol, mixed thoroughly prior to use, and suspended in an ultrasonic bath. To coat the microcarriers for each bombardment, 1 μg of plasmid, 2 μg of dsRNA (1 μl), 12.5 μl of tungsten particle suspension (25 mg/ml), 12.5 μl of 1 M Ca(NO₃)₂ solution (pH 10) were combined dropwise with constant mixing, the mixture was left to stand for 10 minutes at RT and then briefly centrifuged, and 20 μl of the supernatant were drawn off. The remainder with the tungsten particles is resuspended (ultrasonic bath) and employed in the experiment.

Segments (approx. 4 cm in length) of barley primary leaves were used. The tissue was placed on 0.5% Phytagar (GibcoBRL™ Life Technologies™, Karlsruhe) supplemented with 20 μg/ml benzimidazole in Petri dishes (diameter 6.5 cm), and the edges were covered directly prior to particle bombardment with a stencil provided with a rectangular opening of 2.2 cm×2.3 cm. One after the other, the dishes were placed on the bottom of the vacuum chamber (Schweizer P et al. (1999) Mol Plant Microbe Interact 12:647-54) over which a nylon mesh (mesh size 0.2 mm, Millipore, Eschborn) on an apertured plate had been inserted (5 cm above the bottom, 11 cm underneath the macrocarrier, see hereinbelow) to act as diffuser in order to disperse particle aggregates and to slow down the particle stream. For each bombardment, the macrocarrier (plastic syringe filter holder, 13 mm, Gelman Sciences, Swinney, UK), which was attached at the top of the chamber, was loaded with 5.8 μl of DNA-coated tungsten particles (microcarrier, see hereinbelow). The pressure in the chamber was reduced by 0.9 bar using a diaphragm vacuum pump (Vacuubrand, Wertheim), and the surface of the plant tissue was bombarded with the tungsten particles at a helium gas pressure of 9 bar. The chamber was aerated immediately thereafter. To label transformed cells, the leaves were bombarded with the plasmid (pGFP; vector pUC18-based, CaMV ³⁵S promoter/terminator cassette with inserted GFP gene; Schweizer P et al. (1999) Mol Plant Microbe Interact 12:647-54; provided by Dr. P. Schweizer Schweizer P, Institut für Pflanzengenetik [Department of Plant Genetics] IPK, Gatersleben, Germany). Each time before another plasmid was used for the bombardment, the macrocarrier was cleaned thoroughly with water. Following incubation for four hours after the bombardment with slightly open Petri dishes, RT and daylight, the leaves were inoculated with 100 conidia/mm² of the barley powdery mildew fungus (race A6) and incubated for a further 36 to 48 hours under identical conditions.

Leaf segments were bombarded with the coated particles using a particle inflow gun. 312 μg of tungsten particles were applied per bombardment. 4 hours after bombardment, the leaf segments were inoculation inoculated with Blumeria graminis f.sp. hordei mildew (race A6) and, after a further 40 hours, evaluated with regard to infection symptoms. The result (for example the penetration efficacy, defined as percentage of attacked cells with a mature haustorium and a secondary hypha (secondary elongating hyphae) was analyzed by fluorescence and light microscopy. Inoculation with 100 conidia/mm² results in an attack frequency of approximately 50% of the transformed cells. A minimum of 100 interaction sites were evaluated for each individual experiment. Transformed (GFP-expressing) cells were identified under excitation with blue light. Three different categories of transformed cells were distinguished:

-   1. Penetrated cells comprising a readily recognizable haustorium. A     cell with more than one haustorium counted as one cell. -   2. Cells which were attacked by a fungal appressorium, but comprise     no haustorium. A cell which was attacked repeatedly by Bgh, but     contains no haustorium, counted as one cell. -   3. Cells which are not attacked by Bgh.

Stomatal cells and subsidiary cells were excluded from the evaluation. Surface structures of Bgh were analyzed by light microscopy or fluorescent staining of the fungus with 0.1% Calcofluor (w/v in water) for 30 sec. The fungal development can be evaluated readily by staining with Calcofluor followed by fluorescence microscopy. While the fungus develops a primary germ tube and an appressorial germ tube in cells transformed with RacB dsRNA, it fails to develop a haustorium. The development of haustoria is a precondition for the development of a secondary hyphae.

The relative penetration efficacies (RPEs) were calculated as the difference between the penetration efficacies in transformed cells (transformation with RacB dsRNA or control dsRNA) and the penetration efficacies of untransformed cells (here: average penetration efficacy 57%). The percentage RPE (%-RPE) is calculated from the RPE minus 1, multiplied by 100. ${RPE} = \frac{\left\lbrack {{PE}\quad{of}\quad{cells}\quad{transformed}\quad{with}\quad{RacB}\quad{dsRNA}} \right\rbrack}{\left\lbrack {{PE}\quad{of}\quad{cells}\quad{transformed}\quad{with}\quad{control}\quad{dsRNA}} \right\rbrack}$ %-RPE = 100 * (RPE-1)

The %-RPE value (deviation from the average penetration efficacy of the control) serves to determine the susceptibility of cells transfected with RacB dsRNA (FIG. 4).

In the case of the control dsRNA, no difference between the transfection with the control dsRNA and with water was found in five independent experiments with regard to the penetration efficacy of Bgh.

The deviation of the PE in various genotypes was also studied. To demonstrate the operable linkage with the Mlo gene, an mlo5 genotype (A89, mlo5 ror1, background: Ingrid), which owing to a mutation of the Ror1 gene has only moderate susceptibility to Bgh attack (Freialdenhoven et al. (1996) Plant cell 8:5-14), was employed. In this doubly-mutant genotype, the efficacy of RacB dsRNA was studied in comparison with a wild-type Mlo genotype. However, no prevention of the development of haustoria in A89 was observed in five independent experiments, while in parallel experiments with Pallas and Ingrid the PE was markedly reduced (FIG. 5). Interestingly, the effect of the RacB dsRNA was more pronounced in Pallas than in Ingrid (FIG. 5, Experiments 1 and 2 in comparison with 3, 4 and 5).

To rule out an effect of the dsRNA on the transformation rate or survival rate of the attacked cells, the number of GFP-expressing cells was compared between control and RacB dsRNA experiments (Table 7). The RacB dsRNA had no effect on the total number, or the number of attacked, GFP-expressing cells. TABLE 7 Transformation rates of barley leaves following bombardment with dsRNA Number of GFP-expressing cells per bombardment^(a) Total Attacked Attacked (Control (Control Total (RacB (RacB Line dsRNA) dsRNA) dsRNA) dsRNA) n^(c) Pallas 34.3 ± 4.6 16.0 ± 2.2 33.9 ± 4.8 15.5 ± 1.4 6 (21) (Mlo Ror1) Ingrid 51.0 ± 8.9 27.6 ± 8.7 49.9 ± 5.6 31.5 ± 7.8 3 (11) (Mlo Ror1) A89 34.4 ± 5.4 18.1 ± 4.0 34.1 ± 5.5 16.7 ± 3.8 5 (22) (mlo5 ror1)

Example 8 Constitutively Active RACB Mutant

A putatively constitutively active barley RACB mutant (substitution G->V at position 15; RacB-V15) was generated and overexpressed in the barley variety Pallas in order to positively identify RACB as susceptibility factor. First, full-length RACB was synthesized via RT-PCR. The following oligonucleotide primers were employed for this purpose: RacB5′ BamHI 5′-GGATCCGATGAGCGCGTCCAGGTT-3′ (SEQ ID NO: 31) RacB3′ SalI 5′-GTCGACCTTCGCCCTTGTTCTTTGTC-3′ (SEQ ID NO: 32)

The cDNA was cloned into PGEM-T and subsequently excised via the primer cleavage sites and cloned into pGY-1 (Schweizer P et al. (1999) Mol Plant Microbe Interact 12: 647-54; FIG. 7) via BamHI/SalI cleavage sites. The construct is referred to as pGY1-RacB.

The nucleic acid sequence encoding the constitutively active RacB mutant RACB-V15 was generated using the “Transformer®Site-Directed Mutagenesis Kit” (Clonetech, Heidelberg), following the manufacturer's instructions. The starting vector employed was pGY1-RacB. The following oligonucleotide was used as mutagenesis primer: (SEQ ID NO: 33) V15 5′-ACCGTGGGGGACGTCGCCGTCGGCAAGAC-3′

Then, RACB-V15 was then overexpressed transiently in 5 independent experiments in the barley variety Pallas under the control of the ³⁵S CamV promoter. The experiments were carried out as described by Schultheiss et al. (Schultheiss H et al. (2002) Plant Physiol 128:1447-1454), except that, after the particle bombardment, 24 hours instead of 4 hours elapsed prior to inoculation. The particles were coated as described in Schweizer et al. (Schweizer P et al. (1999) Mol Plant Microbe Interact 12:647-54).

The expression of a constitutive RacB mutant brings about a significantly increased susceptibility to pathogen attack by powdery mildew of barley in comparison with the controls. Again, these results confirm the key function of RacB in the defense of pathogens. The RACB-V15 effects. (see FIG. 6-A/B) are significant in the t-test when a two-tail paired test is carried out. The relative susceptibility to the fungal pathogen is increased in all cases (FIG. 6-B).

Example 9 Further HvRac Homologs

All full-length sequences were isolated from RNA using specific primers and cloned into PGEM-T and sequenced (Hückelhoven et al. (2001) Plant Mol Biol; Schultheiss et al. (2002) Plant Physiol 128:1447-1454). In some cases, the sequences are very similar to RacB. a) HvRop6: LEFT PRIMER 5′ -GTGGAGGCGCGGCGAGA-3′ (SEQ ID NO: 25) RIGHT PRIMER 5′ -CCATGCTTCATCTCCATAGTCA-3′ (SEQ ID NO: 26) b) HvRacD: LEFT PRIMER 5′-ggatccCGATTCCATCAGGAAAGCAT-3′ (SEQ ID NO: 27) RIGHT PRIMER 5′-gtcgacGCGAGACACTGCAAAACAAA-3′ (SEQ ID NO: 28) c) HvRop4: LEFT PRIMER 5′-GGATCCttctcgtccatttagccggc-3′ (SEQ ID NO: 29) RIGHT PRIMER 5′-GTCGACtgatcacttgaagcatgccag-3′ (SEQ ID NO: 30)

Example 10 Generation of Sense and Antisense Constructs with the Gene AtRacB for Expression in Arabidopsis thaliana

A fragment of the Arabidopsis RacB homolog (MIPS-Code: AT4g35950; SEQ ID NO: 53; hereinbelow AtRacB) is isolated via PCR from an Arabidopsis thaliana cDNA library. The primer sequences used are: Fra 5′-ATGAGCGCGTCCAGGTTCATA-3′ (SEQ ID NO: 71) 186: Fra 5′-ATCAAACACGCCCTTCACGTT-3′ (SEQ ID NO: 72) 187:

The amplification proceeds in a T3 thermocycler from Biometra with the following temperature profile:

35 cycles of 1 min at 95° C., 0.5 min at 59° C. and 3 min at 72° C. Subsequent extension for 5 min at 72° C.

The PCR products is cloned into the vector pCR2.1 (in accordance with the pCR Script Cloning Kit, Stratagene, Heidelberg) following the manufacturer's instructions. A fragment is excised from the vector construct via the restriction enzyme EcoRI (Roche, Mannheim). The fragment can be isolated via gel electrophoresis and subsequent purification using anion exchanger columns (QIAex Purification Kit, Qiagen, Hilden). Accordingly, the binary vector pSUN3-Nit is opened up via the enzymes XmaI and EcoRI and subjected to purification by means of gel electrophoresis followed by elution over anion exchanger columns (QIAex Purification Kit, Qiagen, Hilden).

Since blunt ends have to be generated for the cloning of insert and vector with 5′-overhangs, both the eluted AtRacB fragment and the eluted pSUN3-Nit fragment are treated with 2 μl of dNTP mix I (10 mM each of dATP, dCTP, dGTP, dTTP; Pharmacia, Freiburg) and 1.6 μl of Klenow fragment (USB/Amersham, Braunschweig, 2 U/μl) for filling up the overhang and incubated for 30 min at 37° C. To prevent religation, the vectors are first purified via a QIAquick Spin Column (Qiagen, Hilden), treated with CIAP (Calf Intestinal Alkaline Phosphatase, GibcoBRL, Eggenstein, 1 U/μl) and finally purified via a 0.8% strength agarose gel.

To prepare the following ligation mix in a total volume of 50 μl, 34 μl of H₂O, 5 μl of ligation buffer and 1 μl of T4 ligase (Roche, Mannheim) are additionally added to the 10 μl of cut DNA. This mixture is incubated overnight at 16° C. The ligase is subsequently inactivated for 10 min at 65° C. The ligation is now followed by precipitation with 0.1 volume of sodium acetate (pH 5.2) and 2.5 volumes of ethanol. After centrifugation (30 min, 15 000 g, 4° C.), the pellet is dried in 70% ethanol and resuspended in 10 μl of H₂O. 2 μl of this pellet are transformed by electroporation (E. coli Pulser, Bio-Rad) into Escherichia coli bacteria, strain DH5α. The DNA-treated bacteria are plated onto LB plates supplemented with the antibiotic ampicillin (50 mg/l). After incubation for 16 h at 37° C., bacteria are scraped from the colonies which have grown and transferred into tubes containing 3 ml of LB-Amp liquid medium each. After incubation for 16 h at 37° C., the cultures, which have grown to great density, are centrifuged. Plasmid DNA is isolated from the bacterial pellets by means of the QIAprep DNA miniprep kit (Qiagen, Hilden) following the manufacturer's instructions and subjected to analytic digests with various enzyme combinations. These control digests allow the isolation of constructs in which the AtRacB gene is cloned in sense or antisense orientation behind the of the A. thaliana nitrilase-1 (nit1) gene, which is constitutively active in plants (GenBank Acc.-No.: Y07648.2, nucleotides 2456-4340, Hillebrand et al. (1996) Gene 170:197-200). These constructs are named pSUN3NIT_AtRacB_s (SEQ ID NO: 73) and pSUN3NIT_atRacB_as (SEQ ID NO: 74) and used for the transformation of Arabidopsis plants. The constructs comprise the complete sequence of AtRacB, so that the expression vector pSUN3NIT_HvRacB_s, which comprises the fragment in sense orientation, is capable of expressing a functional AtRacB protein. The vector acts primarily as negative control and leads in most cases to reduced pathogen resistance, but in some cases (see hereinbelow) also to an increase in pathogen resistance, presumably via a cosuppression effect.

Example 11 Generation of Sense and Antisense Constructs with the Gene HvRacB for Expression in Arabidopsis thaliana

Various nonfunctional fragments of the gene HvRacB are to be prepared for expression in Arabidopsis plants. To this end, the plasmid, which contains the HvRacB gene subcloned into the bacterial vector PGEM-T, is digested with the enzyme combinations BamHI/HindIII (Roche, Mannheim). Overhanging 5′-single strands are filled up by treatment with Klenow polymerase in the presence of a mixture of nucleotides (see above). The resulting HvRacB fragment with these blunt ends is cloned directly into a pSUN3NIT vector, which is opened up with the enzymes BglII and SpeI (Roche, Mannheim) in its multiple cloning site and whose 5′-overhangs are filled up by means of treatment with Klenow polymerase (as described above). For the ligation batches, each of which has a total volume of 50 μl, 34 μl of H₂O, 5 μl of ligation buffer and 1 μl of T4 ligase (Roche, Mannheim) are additionally added to the 10 μl of cut DNA. This mixture is incubated overnight at 16° C. The ligase is subsequently inactivated for 10 min at 65° C. The ligation is now followed by precipitation with 0.1 volume of sodium acetate (pH 5.2) and 2.5 volumes of ethanol. After centrifugation (30 min, 15 000 g, 4° C.), the pellet is dried in 70% ethanol and resuspended in 10 μl of H₂O. 2 μl of this pellet are transformed by electroporation (E. coli Pulser, Bio-Rad) into Escherichia coli bacteria, strain DH5α. The DNA-treated bacteria are plated onto LB plates supplemented with the antibiotic ampicillin (50 mg/l). After incubation for 16 h at 37° C., bacteria are scraped from the colonies which have grown and transferred into tubes containing 3 ml of LB-Amp liquid medium each. After incubation for 16 h at 37° C., the cultures, which have grown to great density, are centrifuged. Plasmid DNA is isolated from the bacterial pellets by means of the QIAprep DNA miniprep kit (Qiagen, Hilden) following the manufacturer's instructions and subjected to analytic digests with various enzyme combinations. These control digests allow the identification of constructs in which the appropriate gene construct is cloned in sense or antisense orientation behind the promoter of the A. thalina nitrilase-1 gene, which is constitutively active in plants (see above). These constructs are named pSUN3NIT_HvRacB_s (SEQ ID NO: 75) and pSUN3NIT_HvRacB_as (SEQ ID NO: 76) and used for the transformation of Arabidopsis plants. The constructs comprise a truncated fragment of hvRacB, so that not even the expression vector pSUN3NIT_HvRacB_s, which comprises the fragment in sense orientation, is capable of expressing a functional HvRacB protein. The vector acts primarily as negative control but leads in some cases (see hereinbelow) also to an increase in pathogen resistance, presumably via a cosuppression effect.

Example 12 Transformation of Arabidopsis thaliana, and Analysis of the Fungal Resistance

Wild-type A. thaliana plants (Columbia) are with the Agrabacterium tumefaciens strain (EHA105) based on a modified method (Steve Clough and Andrew Bent (1998) Plant J 16(6):735-743) of the vacuum infiltration method of Bechtold et al. (Bechtold N et al. (1993) CR Acad Sci Paris, Life Sciences 316:1194-1199).

The A. tumefaciens cells used are previously transformed with the plasmids pSUN3NIT AtRacB_s (SEQ ID NO: 73), pSUN3NIT_atRacB_as (SEQ ID NO: 74), pSUN3NIT_HvRacB_s (SEQ ID NO: 75) and pSUN3NIT_HvRacB_as (SEQ ID NO: 76).

Seeds of the Agrobacterium-transformed primary transformants are selected on the basis of their kanamycin resistance. Antibiotic-resistant seedlings are planted in soil and, when grown into fully developed plants, used for biochemical analysis.

To analyze the resistance of the transgenic Arabidopsis plants to pathogenic fungi, inoculations with the biotrophic fungi Peronospora parasitica and Erysiphe cichoracearum are performed.

a) Peronospora parasitica

Plants aged 5 to 8 weeks are sprayed with a conidia spore suspension (approx. 106 spores/ml). The inoculated plants are kept overnight in a refrigerator at approximately 16° C. under dark and damp conditions, being covered with a plastic bag. After one day, the plastic bag is opened slightly and later removed completely. Six days after inoculation, the plants are again covered with the plastic bag overnight, whereby sporulation is induced. On the next day, the leaves are examined for the appearance of conidiophores. Over the next days, the intercellular growth of the fungus leads to the induction of weak chloroses up to severe necroses in the leaves. These symptoms are quantified and tested for significance.

b) Erysiphe cichoracearum

The biotrophic mildew fungus is grown on Arabidopsis plants. To infect the 4-week-old transgenic RacB-expressing Arabidopsis plants, conidiophores are removed from the leaf surface with a fine brush and applied to the leaves of the transgenic plants. The plants are incubated for 7 days at 20° C. 7 days after the inoculation, the conidiophores appear on the leaves, and chloroses and necroses can be observed over the following days. These symptoms are quantified and tested for significance.

c) Results

The transgenic Arabidopsis plants which express antisense sequences for AtRacB or HvRacB are significantly more resistant to Peronospora parasitica and to Erysiphe cichoracearum than nontransgenic wild-type plants.

The transgenic Arabidopsis plants which express sense sequences for the complete AtRacB are in are in most cases significantly more susceptible to both Peronospora parasitica and Erysiphe cichoracearum than nontransgenic wild-type plants. In some cases, however, an increased resistance can also be observed (presumably via a cosuppression effect).

Transgenic Arabidopsis plants which express sense sequences for the an HvRacB fragment are in are in some cases significantly more resistant to both Peronospora parasitica and Erysiphe cichoracearum than nontransgenic wild-type plants. 

1. A method of generating or increasing a resistance to at least one pathogen in plants, which comprises: reducing an amount, activity or function of an RacB protein in a plant or a tissue, organ, part or cell thereof.
 2. The method of claim 1, wherein the RacB protein is selected from the group consisting of: a polypeptide containing the sequence of SEQ ID NO: 2, 4 or 6; and a functional equivalent of said polypeptide.
 3. The method of claim 2, wherein the functional equivalent has at least 64% homology with the sequence of SEQ ID NO: 2, 4 or
 6. 4. The method of claim 2, wherein the functional equivalent is a polypeptide comprising the sequence of SEQ ID NO: 35, 37, 39, 41, 43, 45, 47, 50, 52, 54, 56, 58, 60, 62, 64, 66, 68 or
 70. 5. The method of claim 1, wherein the reducing comprises introducing to said plant or said tissue, organ, part or cell thereof: a double-stranded RacB RNA or an expression cassette containing or encoding said double-stranded RacB RNA; an RacB antisense nucleic acid or an expression cassette containing or encoding said RacB antisense nucleic acid; an RacB antisense nucleic acid in combination with a ribozyme or an expression cassette containing or encoding said RacB antisense nucleic acid and said ribozyme; a RacB sense nucleic acid for inducing cosuppression or an expression cassette containing or encoding said RacB sense nucleic acid; a nucleic acid encoding a dominant-negative RacB protein or an expression cassette containing said nucleic acid; a DNA- or protein-binding factor against RacB genes, RacB RNAs or RacB protein or an expression cassette capable of expressing said DNA- or protein-binding factor; a viral nucleic acid and an expression construct that causes RacB RNA degradation or an expression cassette containing said viral nucleic acid and said expression construct; a construct for inducing a homologous recombination of an endogenous RacB gene; a mutation of the endogenous RacB gene; or a combination thereof.
 6. The method of claim 1, comprising: stably transforming a plant cell with a recombinant expression cassette comprising a nucleic acid encoding; a double-stranded RacB RNA; an RacB antisense nucleic acid, an RacB antisense nucleic acid combined with a ribozyme, an RacB sense nucleic acid for inducing cosuppression, a dominant-negative RacB protein, a DNA- or protein-binding factor against a RacB gene, a RacB RNA, or a RacB protein, a viral nucleic acid that causes RacB RNA degradation in operable linkage with a promoter which is active in said plant or said tissue, organ, part or cell thereof, or a combination thereof; regenerating a plant from the plant cell; and expressing said nucleic acid in an amount and over a period of time sufficient to generate or increase said resistance.
 7. The method of claim 1, wherein the at least one pathogen is selected from the group consisting of bacteria, fungi, insects, viruses, nematodes, and combinations thereof.
 8. The method of claim 7, wherein the fungi is selected from the group consisting of Plasmodiophoramycota, Oomycota, Ascomycota, Chytridiomycetes, Zygomycetes, Basidiomycota, Deuteromycetes, and combinations thereof.
 9. The method of claim 1, wherein the plant or the tissue, organ, part or cell thereof is selected or derived from a monocot or a dicot.
 10. The method of claim 9, wherein the monocot is selected from the group consisting of wheat, oats, millet, barley, rye, maize, rice, buckwheat, sorghum, triticale, spelt, linseed, sugar cane, and combinations thereof.
 11. An isolated barley RacB protein that contains the sequence of SEQ ID NO:
 2. 12. An isolated polypeptide that comprises a functional equivalent of a barley RacB protein.
 13. The barley RacB protein of claim 11, which is a dominant-negative variant.
 14. The barley RacB protein of claim 13, which contains the sequence of SEQ ID NO:
 7. 15. An isolated nucleic acid encoding the barley RacB protein of claim
 11. 16. An isolated nucleic acid that contains the sequence of SEQ ID NO: 1, a sequence complementary thereto, or a sequence derived from said sequence or said complementary sequence by degeneracy of the genetic code.
 17. An isolated nucleic acid encoding the barley RacB protein of claim
 12. 18. An isolated nucleic acid that contains the sequence of SEQ ID NO: 34, 36 or 38, a sequence complementary thereto, or a sequence derived from said sequence of SEQ ID NO: 34, 36 or 38, or said complementary sequence by degeneracy of the genetic code.
 19. An isolated nucleic acid encoding the RacB protein of claim
 13. 20. A recombinant double-stranded RNA molecule that is capable of reducing expression of an RacB protein, wherein: one of the two RNA strands of said molecule is essentially identical to at least part of a nucleic acid that encodes said RacB protein; and the other RNA strand of said molecule is essentially identical to at least part of the complementary strand of said nucleic acid.
 21. A recombinant double-stranded RNA molecule that is capable of reducing expression of an RacB protein, comprising: a sense strand comprising a sequence which is essentially identical to at least part of the sense RNA transcript of a sequence encoding the RacB protein; and an antisense strand, which is essentially complementary to the sense strand.
 22. The dsRNA molecule of claim 20, wherein the two RNA strands are linked covalently to each other.
 23. The dsRNA molecule of claim 20, wherein one of the two RNA strands comprises the sequence of SEQ ID NO: 1, 3 or 5, or of a functional equivalent thereof.
 24. A transgenic expression cassette comprising the nucleic acid of claim 15 in operable linkage with a promoter.
 25. A transgenic expression cassette comprising at least part of a nucleic acid sequence encoding an RacB protein wherein said nucleic acid sequence is operably linked and in antisense orientation to a promoter.
 26. The transgenic expression cassette of claim 24, wherein the promoter is functional in a plant.
 27. The transgenic expression cassette of claim 26, wherein the promoter is a pathogen-inducible promoter.
 28. A transgenic vector comprising the expression cassette of claim
 24. 29. A transgenic organism comprising the nucleic acid of claim
 15. 30. The transgenic organism of claim 29, wherein the organism is selected from the group of organisms consisting of bacteria, yeasts, animals and plants.
 31. The transgenic organism of claim 30, wherein the plants are selected from the group consisting of wheat, oats, millet, barley, rye, maize, rice, buckwheat, sorghum, triticale, spelt, linseed, sugar cane, oil seed rape, canola, cress, Arabidopsis, cabbages, soya, alfalfa, pea, beans, peanut, potato, tobacco, tomato, eggplant, bell pepper, sunflower, Tagetes, lettuce, Calendula, melon, pumpkin/squash and zucchini.
 32. A plant or a tissue, organ, part or cell thereof made by the method of claim
 1. 33. A stably transformed plant cell made by the method of claim
 6. 34. The method of claim 1, wherein activity comprises GTPase activity of said RacB protein.
 35. The method of claim 1, wherein function comprises a substrate-binding capacity of said RacB protein.
 36. A method of selecting a plant cell with an increased resistance to a pathogen comprising: introducing a nucleic acid to plant cells that reduces an amount, activity or function of an RacB protein of said plant cells; and selecting at least one of said plant cells wherein resistance to said pathogen is increased as compared to untransformed cells.
 37. The method of claim 36, wherein activity comprises GTPase activity of said RacB protein.
 38. The method of claim 36, wherein function comprises a substrate-binding capacity of said RacB protein.
 39. The polypeptide of claim 12, which contains the sequence of SEQ ID NO: 35, 37 or
 39. 40. The dsRNA molecule of claim 23, wherein the functional equivalent contains the sequence of SEQ ID NO: 34, 36, 38, 40, 42, 44, 46, 48, 49, 51, 53, 55, 57, 61, 63, 65, 67 or
 69. 41. A transgenic expression cassette comprising a nucleic acid encoding a dsRNA molecule of claim 20 in operable linkage with a promoter.
 42. A transgenic expression cassette comprising at least part of a functional equivalent of a nucleic acid encoding an RacB protein, which is operably linked and in antisense orientation to a promoter.
 43. The transgenic expression cassette of claim 42, which comprises the sequence of SEQ ID NO: 34, 36, 38, 40, 42, 44, 46, 48, 49, 51, 53, 55, 57, 61, 63, 65, 67 or
 69. 44. A transgenic organism comprising the dsRNA of claim
 20. 45. A transgenic organism comprising the expression cassette of claim
 24. 46. The transgenic expression cassette of claim 25, which contains the sequence of SEQ ID NO: 1, 3 or
 5. 47. A transgenic organism comprising the vector of claim
 28. 48. A recombinant plant cell wherein an expressed amount, activity or function of an endogenous RacB protein is reduced by stable transformation with a nucleic acid as compared to an untransformed cell.
 49. The cell of claim 48, wherein activity comprises GTPase activity of said RacB protein.
 50. The cell of claim 48, wherein function comprises a substrate-binding capacity of said RacB protein.
 51. The cell of claim 48, wherein the reduction is at least 60%.
 52. The cell of claim 48, wherein the reduction is at least 90%.
 53. The cell of claim 48, wherein the nucleic acid comprises a double-stranded RNA molecule that contains a sense strand comprising a sequence which is essentially identical to at least part of the sense RNA transcript of a sequence encoding the RacB protein; and an antisense strand which is essentially complementary to the sense strand.
 54. The cell of claim 48, wherein the nucleic acid comprises: a double-stranded RacB RNA; an RacB antisense nucleic acid; an RacB antisense nucleic acid combined with a ribozyme; an RacB sense nucleic acid for inducing cosuppression; a sequence that encodes a dominant-negative RacB protein; a sequence that encodes a DNA- or protein-binding factor against a RacB gene, a RacB RNA, or the RacB protein; a viral nucleic acid that causes RacB RNA degradation in operable linkage with a promoter which is active in said plant cell, or a combination thereof.
 55. The cell of claim 48, wherein the nucleic acid comprises the sequence of SEQ ID NO: 1, 3, 5, 34, 36, 38, 39, 40, 42, 44, 46, 48, 49, 53, 55, 57, 59, 61, 63, 65, 67 or 79, or a part thereof.
 56. The cell of claim 48, wherein the reduction provides said cell with an increased resistance to a pathogen as compared to an untransformed cell.
 57. The cell of claim 56, wherein the pathogen is selected from the group consisting of bacteria, fungi, insects, viruses, nematodes, and combinations thereof.
 58. The method of claim 2, wherein the functional equivalent of said polypeptide is another polypeptide that has a capability of conferring a pathogen-resistant phenotype or an increased resistance to at least one pathogen, to said plant or said tissue, organ, part or cell thereof.
 59. The polypeptide of claim 12, wherein the functional equivalent of said Barley RacB protein is capable of conferring a pathogen-resistant phenotype or an increased resistance to at least one pathogen, to a plant or a tissue, organ, part or cell thereof.
 60. The polypeptide of claim 12, wherein the functional equivalent of said Barley RacB protein has a sequence which is at least 60% homologous with the sequence of SEQ ID NO 2, 4, or
 6. 61. The polypeptide of claim 12, wherein the functional equivalent of said Barley RacB protein has a sequence which is at least 80% homologous with the sequence of SEQ ID NO 2, 4, or
 6. 62. The polypeptide of claim 12, wherein the functional equivalent of said Barley RacB protein has a sequence which is at least 90% homologous with the sequence of SEQ ID NO 2, 4, or
 6. 63. An isolated nucleic acid that encodes the sequence of the polypeptide of claim
 12. 64. An isolated dominant-negative variant of a barley RacB protein that contains the sequence of SEQ ID NO:
 2. 65. A functional equivalent of the barley RacB protein of claim
 64. 66. The variant of claim 64, which contains the sequence of SEQ ID NO:
 7. 67. An isolated nucleic acid encoding the variant of claim
 64. 68. The dsRNA molecule of claim 21, wherein the two RNA strands are linked covalently to each other.
 69. The dsRNA molecule of claim 21, wherein one of the two RNA strands comprises the sequence of SEQ ID NO: 1, 3 or 5, or of a functional equivalent thereof.
 70. The dsRNA molecule of claim 69, wherein the functional equivalent contains the sequence of SEQ ID NO: 34, 36, 38, 40, 42, 44, 46, 48, 49, 51, 53, 55, 57, 61, 63, 65, 67 or
 69. 71. A transgenic expression cassette comprising a nucleic acid encoding a dsRNA molecule of claim 21 in operable linkage with a promoter.
 72. A transgenic organism comprising the dsRNA of claim
 21. 